Organization and Business - Narrative (Details)								9 Months Ended	27 Months Ended	31 Months Ended
Organization and Business - Narrative (Details)	Jul. 26, 2021 USD ($) $ / shares Rate shares	Aug. 31, 2020 USD ($) $ / shares shares	Mar. 06, 2020 USD ($) apartment_home joint_venture multifamily_property $ / shares shares	Mar. 24, 2016 USD ($) shares	Dec. 30, 2013 $ / shares shares	Sep. 03, 2013 USD ($) $ / shares shares	Aug. 22, 2013 USD ($) shares	Sep. 30, 2021 USD ($) apartment_home multifamily_property parcel_of_land $ / shares shares	Mar. 24, 2016 USD ($) shares	Mar. 24, 2016 USD ($) shares	Apr. 01, 2021 $ / shares	Dec. 31, 2020 $ / shares	May 01, 2020 $ / shares
Initial capitalization
Recapitalization exchange ratio \| Rate	90.50%
Share Repurchase Plan As Amended
Initial capitalization
Notice period for amendment, suspension, or termination of share repurchase plan								30 days
Garrison Station
Initial capitalization
Number of multifamily properties \| multifamily_property								9
Number of apartment homes, in service \| apartment_home								160
Number of buildings, in service \| multifamily_property								8
Number of apartment homes \| apartment_home								176
Letter Agreement \| Uninsured Risk
Initial capitalization
Self-insurance retention \| $	$ 1,000,000
Indemnification Agreement \| Letter Agreement
Initial capitalization
Percentage of maximum exposure	75.00%
SIR and STAR III Merger Agreement
Initial capitalization
Gross real estate assets \| $			$ 1,500,000,000
SIR Merger Agreement
Initial capitalization
Stock, par value (in dollars per share) \| $ / shares			$ 0.01
Entity shares issued per acquiree share (in shares)			0.5934
STAR III Merger Agreement
Initial capitalization
Stock, par value (in dollars per share) \| $ / shares			$ 0.01
Entity shares issued per acquiree share (in shares)			1.430
Distribution Reinvestment Plan
Initial capitalization
Notice period for termination of plan	10 days							10 days
Multifamily
Initial capitalization
Number of multifamily properties \| multifamily_property								70
Multifamily \| SIR and STAR III Merger Agreement
Initial capitalization
Number of multifamily properties \| multifamily_property			36
Residential Real Estate
Initial capitalization
Number of parcels of land held for development \| parcel_of_land								3
Homes \| apartment_home								22,001
Residential Real Estate \| SIR and STAR III Merger Agreement
Initial capitalization
Homes \| apartment_home			10,166
Unconsolidated Properties \| SIR and STAR III Merger Agreement
Initial capitalization
Number of apartment homes \| apartment_home			4,584
Number of unconsolidated joint ventures \| joint_venture			1
Unconsolidated Properties \| Joint Venture \| SIR and STAR III Merger Agreement
Initial capitalization
Number of multifamily properties \| multifamily_property			20
Unconsolidated Properties \| Steadfast Apartment REIT, Inc. \| SIR and STAR III Merger Agreement
Initial capitalization
Noncontrolling interest, ownership percentage			10.00%
Common Stock
Initial capitalization
Share price (in dollars per share) \| $ / shares								$ 0.525
Stock, par value (in dollars per share) \| $ / shares	$ 0.01							$ 0.01				$ 0.01
Common Stock \| SIR and STAR III Merger Agreement
Initial capitalization
Issuance of common stock (in shares)			56,016,053
Common Stock \| Primary Offering
Initial capitalization
Share price (in dollars per share) \| $ / shares					$ 15.00
Maximum number of shares authorized for sale under registration statement (in shares)					66,666,667
Common Stock \| Distribution Reinvestment Plan
Initial capitalization
Issuance of common stock (in shares)								8,669,192	1,011,561
Share price (in dollars per share) \| $ / shares					$ 14.25						$ 15.55		$ 15.23
Maximum number of shares authorized for sale under registration statement (in shares)					7,017,544
Proceeds from issuance of common stock \| $								$ 130,065,017	$ 14,414,752
Common Stock \| Distribution Reinvestment Plan \| Share Repurchase Plan As Amended
Initial capitalization
Share price (in dollars per share) \| $ / shares								$ 15.55
Common Stock \| IPO
Initial capitalization
Issuance of common stock (in shares)				48,625,651				112,299,272		48,625,651
Proceeds from issuance of common stock \| $				$ 724,849,631				$ 1,727,794,175		$ 640,012,497
Convertible Stock
Initial capitalization
Stock, par value (in dollars per share) \| $ / shares								$ 0.01				0.01
Class A Convertible Stock
Initial capitalization
Promote price \| $		$ 1,000
Stock, par value (in dollars per share) \| $ / shares								$ 0.01				$ 0.01
Class B OP Units \| Indemnification Agreement \| Letter Agreement
Initial capitalization
Number of shares held (in shares)	1,277,778
Operating Partnership Units
Initial capitalization
Ownership percentage								94.00%
Sponsor \| Common Stock
Initial capitalization
Issuance of common stock (in shares)						13,500
Share price (in dollars per share) \| $ / shares						$ 15.00
Issuance of common stock \| $						$ 202,500
Sponsor \| Common Stock \| SIR Merger Agreement
Initial capitalization
Issuance of common stock (in shares)			43,775,314
Sponsor \| Common Stock \| STAR III Merger Agreement
Initial capitalization
Issuance of common stock (in shares)			12,240,739
Advisor \| Convertible Stock
Initial capitalization
Issuance of common stock (in shares)							1,000
Issuance of common stock \| $							$ 1,000
STAR RS Holdings, LLC (SRSH)
Initial capitalization
Share price (in dollars per share) \| $ / shares		$ 15.23
Value of consideration transferred excluding convertible shares \| $		$ 124,999,000
Cash consideration \| $		$ 31,249,000
Fair value per Class B OP Unit (in dollars per share) \| $ / shares		$ 15.23
STAR RS Holdings, LLC (SRSH) \| Common Stock
Initial capitalization
Issuance of common stock (in shares)								56,016,053
STAR RS Holdings, LLC (SRSH) \| Class A Convertible Stock
Initial capitalization
Promote price \| $		$ 1,000
STAR RS Holdings, LLC (SRSH) \| Class B OP Units
Initial capitalization
Class B OP Units issued (in shares)		6,155,613.92						6,155,613.92
Steadfast Apartment REIT, Inc. \| SIR Merger Agreement
Initial capitalization
Entity shares issued per acquiree share (in shares)			1.430
Steadfast Apartment REIT, Inc. \| STAR III Merger Agreement
Initial capitalization
Entity shares issued per acquiree share (in shares)			0.5934
SRI and Affiliates \| Operating Partnership Units
Initial capitalization
Ownership percentage								5.00%
Unaffiliated Third Parties \| Operating Partnership Units
Initial capitalization
Ownership percentage								1.00%
Independent Realty Trust, Inc. \| Common Stock
Initial capitalization
Stock, par value (in dollars per share) \| $ / shares	$ 0.01
Number of shares issued during period (in shares)	1
Number of shares issued in exchange for stock previously held (in shares)	99,700,000
Independence Realty Operating Partnership, LP \| IROP Common Units
Initial capitalization
Number of shares issued in exchange for stock previously held (in shares)	6,400,000
Sponsor \| Indemnification Agreement \| Letter Agreement
Initial capitalization
Amount of maximum exposure \| $	$ 20,300,000

Steadfast Apartment REIT, Inc. 10-Q