Fair Value Measurements (Details 1) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investments, at fair value (Beginning Balance)	$ 50,752	$ 404,365	$ 404,365
Total investments, at fair value, Initial Consolidation		0
Total investments, at fair value, Purchases/Issuances		123,951
Total investments, at fair value, Sales/Redemptions/Settlements		(78,690)
Total investments, at fair value, Total Realized and Change in Unrealized Gains (Losses)		(15)
Total investments, at fair value, Amortization of Discounts/Premiums		340
Total investments, at fair value, Transfers to (from) Level 3		0
Total investments, at fair value (Ending Balance)	30,121	449,951	50,752
Total investments, at fair value, Assets Measured on Recurring Basis, Change in Unrealized Gains/Losses Relating to Assets and Liabilities Still Held		867
Total liabilities, at fair value (Beginning Balance)		384,901	384,901
Total liabilities, at fair value, Effect of Deconsolidation		0
Total liabilities, at fair value, Purchases/Issuances		0
Total liabilities, at fair value, Sales/Redemptions/Settlements		0
Total liabilities, at fair value, Realized and Unrealized Gains/Losses		0
Total liabilities, at fair value, Amortization of Discounts/Premiums		6,727
Total liabilities, at fair value, Transfers		0
Total liabilities, at fair value (Ending Balance)		391,628
Total liabilities, at fair value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		6,727
Warehouse [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investments, at fair value (Beginning Balance)	50,752	15,036	15,036
Total investments, at fair value, Initial Consolidation		0
Total investments, at fair value, Sales/Redemptions/Settlements		30,000
Total investments, at fair value, Total Realized and Change in Unrealized Gains (Losses)		0
Total investments, at fair value, Amortization of Discounts/Premiums		1,107
Total investments, at fair value, Amortization of Discounts/Premiums		0
Total investments, at fair value, Transfers to (from) Level 3		0
Total investments, at fair value (Ending Balance)	30,121	46,143	50,752
Total investments, at fair value, Assets Measured on Recurring Basis, Change in Unrealized Gains/Losses Relating to Assets and Liabilities Still Held		1,107
Notes Payable of Consolidated CLOs [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total liabilities, at fair value (Beginning Balance)		384,901	384,901
Total liabilities, at fair value, Effect of Deconsolidation		0
Total liabilities, at fair value, Purchases/Issuances		0
Total liabilities, at fair value, Sales/Redemptions/Settlements		0
Total liabilities, at fair value, Realized and Unrealized Gains/Losses		0
Total liabilities, at fair value, Amortization of Discounts/Premiums		6,727
Total liabilities, at fair value, Transfers		0
Total liabilities, at fair value (Ending Balance)		391,628
Total liabilities, at fair value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		6,727
First Lien Senior Secured Loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investments, at fair value (Beginning Balance)		389,329	389,329
Total investments, at fair value, Initial Consolidation		0
Total investments, at fair value, Purchases/Issuances		93,951
Total investments, at fair value, Sales/Redemptions/Settlements		(78,690)
Total investments, at fair value, Total Realized and Change in Unrealized Gains (Losses)		(1,122)
Total investments, at fair value, Amortization of Discounts/Premiums		340
Total investments, at fair value, Transfers to (from) Level 3		0
Total investments, at fair value (Ending Balance)		403,808
Total investments, at fair value, Assets Measured on Recurring Basis, Change in Unrealized Gains/Losses Relating to Assets and Liabilities Still Held		$ (240)
Collateralized Loan Obligations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investments, at fair value (Beginning Balance)	114,911
Total investments, at fair value, Purchases/Issuances	55,350
Total investments, at fair value, Sales/Redemptions/Settlements	(55,067)
Total investments, at fair value, Total Realized and Change in Unrealized Gains (Losses)	2,130
Total investments, at fair value, Amortization of Discounts/Premiums	(129)
Total investments, at fair value, Effect of Deconsolidation	0
Total investments, at fair value (Ending Balance)	117,195		114,911
Total investments, at fair value, Assets Measured on Recurring Basis, Change in Unrealized Gains/Losses Relating to Assets and Liabilities Still Held	(477)
Collateralized Loan Obligations [Member] \| Warehouse [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investments, at fair value (Beginning Balance)	50,752
Total investments, at fair value, Purchases/Issuances	32,500
Total investments, at fair value, Sales/Redemptions/Settlements	(55,067)
Total investments, at fair value, Total Realized and Change in Unrealized Gains (Losses)	1,936
Total investments, at fair value, Amortization of Discounts/Premiums	0
Total investments, at fair value, Effect of Deconsolidation	0
Total investments, at fair value (Ending Balance)	30,121		50,752
Total investments, at fair value, Assets Measured on Recurring Basis, Change in Unrealized Gains/Losses Relating to Assets and Liabilities Still Held	(631)
Collateralized Loan Obligations [Member] \| Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investments, at fair value (Beginning Balance)	34,588
Total investments, at fair value, Purchases/Issuances	14,174
Total investments, at fair value, Sales/Redemptions/Settlements	0
Total investments, at fair value, Total Realized and Change in Unrealized Gains (Losses)	74
Total investments, at fair value, Amortization of Discounts/Premiums	0
Total investments, at fair value, Effect of Deconsolidation	0
Total investments, at fair value, Transfers to (from) Level 3	48,836
Total investments, at fair value (Ending Balance)	(74)		34,588
Collateralized Loan Obligations [Member] \| Mezzanine Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investments, at fair value (Beginning Balance)	24,695
Total investments, at fair value, Purchases/Issuances	6,825
Total investments, at fair value, Sales/Redemptions/Settlements	0
Total investments, at fair value, Total Realized and Change in Unrealized Gains (Losses)	(99)
Total investments, at fair value, Amortization of Discounts/Premiums	142
Total investments, at fair value, Effect of Deconsolidation	0
Total investments, at fair value, Transfers to (from) Level 3	31,563
Total investments, at fair value (Ending Balance)	(99)		24,695
Collateralized Loan Obligations [Member] \| Subordinated Debt [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investments, at fair value (Beginning Balance)	4,876
Total investments, at fair value, Purchases/Issuances	1,851
Total investments, at fair value, Sales/Redemptions/Settlements	0
Total investments, at fair value, Total Realized and Change in Unrealized Gains (Losses)	219
Total investments, at fair value, Amortization of Discounts/Premiums	(271)
Total investments, at fair value, Effect of Deconsolidation	0
Total investments, at fair value, Transfers to (from) Level 3	6,675
Total investments, at fair value (Ending Balance)	$ 179		$ 4,876

ZAIS Group Holdings, Inc. 10-Q