Carver Bancorp Inc.-Parent Company Only Carver Bancorp Inc.-Parent Company Only Text Tag (Details) - USD ($) $ in Thousands		3 Months Ended									12 Months Ended
		Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2017	Mar. 31, 2016		Mar. 31, 2015	[7]
Other liabilities		$ 11,884				$ 12,030	[1],[2]				$ 11,884	$ 12,030	[1],[2]
Total assets		687,861				739,054	[1]				687,861	739,054	[1]
Total liabilities		640,463				687,174	[1]				640,463	687,174	[1]
Total liabilities and equity		687,861				739,054	[2],[3]				687,861	739,054	[2],[3]
Interest expense on borrowings											1,257	1,336	[2],[4]
Net loss		(2,034)	$ (893)	$ (251)	$ 325	(1,489)		$ 156	$ (563)	$ 129	(2,853)	(1,767)	[2],[3],[5]
Comprehensive loss											(4,486)	(1,029)	[2]
Increase in other liabilities											(147)	1,470	[3],[5]
Total equity		47,398				51,880	[2],[3],[6]				47,398	51,880	[2],[3],[6]	$ 52,907
Restatement Adjustment
Other liabilities						(339)						(339)
Total assets						(2,674)						(2,674)
Total liabilities						(339)						(339)
Total liabilities and equity						(2,674)						(2,674)
Interest expense on borrowings												66
Net loss			$ 263	$ 1	$ (83)	(460)		$ (414)	$ (407)	$ (316)		(1,597)
Comprehensive loss												(1,597)
Increase in other liabilities												(540)
Total equity						(2,335)						(2,335)
Parent Company
Investment in subsidiaries		60,921				64,597	[3]				60,921	64,597	[3]
Other liabilities		399				2,327	[8]				399	2,327	[8]
Total assets		61,428				67,661	[3]				61,428	67,661	[3]
Total liabilities		14,030				15,781	[8]				14,030	15,781	[8]
Total liabilities and equity		61,428				67,661	[3]				61,428	67,661	[3]
Equity in net loss from subsidiaries											2,048	767	[6],[9]
Interest expense on borrowings											568	531	[5]
Total income											(2,022)	(744)	[9]
Total expense											831	1,023	[10]
Net loss											(2,853)	(1,767)	[6],[9]
Increase in other liabilities											(1,928)	530
Total equity		$ 47,398				51,880	[3]				$ 47,398	51,880	[3]
Parent Company | Restatement Adjustment
Investment in subsidiaries	[3]					(2,200)						(2,200)
Other liabilities						157						157
Total assets						(2,200)						(2,200)
Total liabilities						157						157
Total liabilities and equity						(2,200)						(2,200)
Equity in net loss from subsidiaries												1,500
Interest expense on borrowings												66
Total income												(1,500)
Total expense												66
Net loss												(1,600)
Comprehensive loss												(1,600)
Increase in other liabilities												66
Total equity						$ (2,300)						$ (2,300)

[1] (1) March 31, 2016 balances have been restated from previously reported results to correct for material and certain other errors from prior periods. Equity in net loss from subsidiaries was increased and total income was reduced by $1.5 million, interest expense on borrowings and total expense were increased by $66 thousand, and net loss and comprehensive loss were increased $1.6 million. Refer to Notes 1 and 19 for further detail.

[2] (1) March 31, 2016 balances have been restated from previously reported results to correct for material and certain other errors from prior periods. Refer to Notes 1 and 19 for further detail.

[3] (1) March 31, 2015 and 2016 balances have been restated from previously reported results to correct for material and certain other errors from prior periods. Refer to Notes 1 and 19 for further detail.

[4] (a) March 31, 2016 balances have been restated from previously reported results to correct for material and certain other errors from prior periods. Refer to Notes 1 and 19 for further detail.

[5] (1) March 31, 2016 balances have been restated from previously reported results to correct for material and certain other errors from prior periods. Net loss was increased by $1.6 million, equity in net loss of subsidiaries was increased by $1.5 million and increase in other liabilities was increased by $66 thousand. Refer to Notes 1 and 19 for further detail.

[6] (1) March 31, 2016 balances have been restated from previously reported results to correct for material and certain other errors from prior periods. Refer to Notes 1 and 19 for further detail.

[7] (1) March 31, 2016 balances have been restated from previously reported results to correct for material and certain other errors from prior periods. Refer to Notes 1 and 19 for further detail.

[8] (1) March 31, 2016 balances have been restated from previously reported results to correct for material and certain other errors from prior periods. Refer to Notes 1 and 19 for further detail.

[9] (1) March 31, 2016 balances have been restated from previously reported results to correct for material and certain other errors from prior periods. Refer to Notes 1 and 19 for further detail.

[10] (1) March 31, 2016 balances have been restated from previously reported results to correct for material and certain other errors from prior periods. Investment in subsidiaries, total assets and total liabilities and stockholders' equity were each reduced by $2.2 million, other liabilities and total liabilities increased by $157 thousand and stockholders' equity was reduced by $2.3 million. Refer to Notes 1 and 19 for further detail.