Fair Value Measurements (Reconciliation of Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value of warrants at beginning of year	$ 149
Unrealized gain (loss) on fair valuation of warrants	4	$ (10)
Fair value of warrants at end of year	153	149
Unrealized gain on fair valuation of investment in securities	5
Fair value of investment in securities at end of year	27
Level 3 Estimated Fair Value [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value of warrants at beginning of year	149	159
Unrealized gain (loss) on fair valuation of warrants	4	(10)
Fair value of warrants at end of year	153	149
Level 1 Estimated Fair Value [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value of investment in securities at beginning of year	22
Unrealized gain on fair valuation of investment in securities	5
Fair value of investment in securities at end of year	$ 27	$ 22

ATEL 12, LLC 10-K