Carver Bancorp Inc.- Parent Company Only-Condensed Statements of Cash Flow (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2003
Condensed Cash Flow Statements, Captions [Line Items]
Net loss	$ (1,798)	$ (1,436)	$ (1,050)	$ (1,139)	$ (1,540)	$ (1,349)	$ (2,017)	$ (1,030)	$ (5,423)	$ (5,936)
Decrease (increase) in other assets									3,397	(1,995)
Decrease in other liabilities									(134)	(1,675)
Net cash (used in) provided by operating activities									(31)	(8,765)
Proceeds from (Payments for) Other Financing Activities											$ 400
Net cash provided by financing activities									619	(123,687)
Parent Company
Condensed Cash Flow Statements, Captions [Line Items]
Net loss									(5,423)	(5,936)
Equity in net loss from subsidiaries									(4,499)	(4,968)
Increase in account receivable from subsidiaries									4	30
Decrease (increase) in other assets									(36)	(25)
Increase (decrease) in accounts payable to subsidiaries									176	170
Decrease in other liabilities									785	824
Net cash (used in) provided by operating activities									(3)	(29)
Proceeds from (Payments for) Other Financing Activities									4	30
Net cash provided by financing activities									4	30
Net decrease in cash									1	1
Cash and cash equivalents - beginning				$ 495				$ 494	495	494
Cash and cash equivalents - end	$ 496				$ 495				$ 496	$ 495