Carver Bancorp Inc.- Parent Company Only-Condensed Statements of Cash Flow (Details) - USD ($) $ in Thousands	3 Months Ended									12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 1994	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2003
Condensed Cash Flow Statements, Captions [Line Items]
Net loss	$ (965)	$ (1,310)	$ (809)	$ (812)	$ (1,798)	$ (1,436)	$ (1,050)	$ (1,139)		$ (3,896)	$ (5,423)
Increase (Decrease) in Other Operating Assets										593	3,397
Increase (Decrease) in Other Operating Liabilities										5,192	(134)
Net cash (used in) provided by operating activities										2,212	(31)
Proceeds from Other Equity										2,500
Payments for Repurchase of Common Stock										(2,500)
Proceeds from Issuance of Common Stock									$ 21,500	3,197
Proceeds from Issuance of Preferred Stock and Preference Stock										8,177
Proceeds from (Payments for) Other Financing Activities												$ 400
Net cash provided by financing activities										102,823	619
Parent Company
Condensed Cash Flow Statements, Captions [Line Items]
Net loss										(3,896)	(5,423)
Equity in net loss from subsidiaries										(3,039)	(4,499)
Increase in account receivable from subsidiaries										164	4
Increase (Decrease) in Other Operating Assets										(38)	(36)
Increase (decrease) in accounts payable to subsidiaries										917	176
Increase (Decrease) in Other Operating Liabilities										609	785
Net cash (used in) provided by operating activities										467	(3)
Proceeds from Other Equity										2,500	0
Payments for Repurchase of Common Stock										(2,500)	0
Proceeds from Issuance of Common Stock										3,197	0
Proceeds from Issuance of Preferred Stock and Preference Stock										8,177	0
Proceeds from (Payments for) Other Financing Activities										37	4
Net cash provided by financing activities										11,411	4
Net decrease in cash										11,878	1
Cash and cash equivalents - beginning				$ 496				$ 495		496	495
Cash and cash equivalents - end	$ 12,374				$ 496					$ 12,374	$ 496