Borrowings (Interest Rates and Company Borrowings) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Interest and debt expense:
Weighted average interest rate during the quarter	1.39%	1.67%	1.38%	1.67%
Interest rate at quarter end	1.38%	1.67%	1.38%	1.67%
Maximum amount outstanding during the quarter	$ 1,093,000	$ 1,105,000	$ 1,093,000	$ 1,175,000
Average amount outstanding during the quarter	1,090,283	1,059,130	1,081,716	1,109,978
Facility fees	$ 61	$ 90	$ 131	$ 94