Carver Bancorp Inc.-Parent Company Only Parent Company Only-Condensed Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2019	Mar. 31, 2018
Condensed Income Statements, Captions [Line Items]
Interest expense on borrowings									$ 909	$ 1,174
Salaries and employee benefits									12,248	12,615
Shareholder expense									313	346
Other									7,474	7,660
Net (loss) income	$ (1,540)	$ (1,349)	$ (2,017)	$ (1,030)	$ 7,533	$ (944)	$ (594)	$ (641)	(5,936)	5,354
Comprehensive loss									(4,870)	4,568
Parent Company
Condensed Income Statements, Captions [Line Items]
Equity in net loss from subsidiaries									(4,968)	6,097
Other income									26	20
Total income									(4,942)	6,117
Interest expense on borrowings									819	624
Shareholder expense									73	49
Other									102	90
Total expense									994	763
Net (loss) income									$ (5,936)	$ 5,354