Carver Bancorp Inc.- Parent Company Only-Condensed Statements of Operations (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
Condensed Income Statements, Captions [Line Items]
Interest expense on borrowings									$ 991	$ 909
Salaries and employee benefits									11,372	12,248
Shareholder expense									331	313
Other									5,606	7,398
Net loss	$ (1,798)	$ (1,436)	$ (1,050)	$ (1,139)	$ (1,540)	$ (1,349)	$ (2,017)	$ (1,030)	(5,423)	(5,936)
Comprehensive loss									(3,552)	(4,870)
Parent Company
Condensed Income Statements, Captions [Line Items]
Equity in net loss from subsidiaries									(4,499)	(4,968)
Other income									26	26
Total income									(4,473)	(4,942)
Interest expense on borrowings									815	819
Shareholder expense									32	73
Other									103	102
Total expense									950	994
Net loss									$ (5,423)	$ (5,936)