Borrowings (Interest Rates and Company Borrowings) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Interest and debt expense:
Weighted average interest rate during the quarter	1.67%	3.50%	1.67%	3.61%
Interest rate at quarter end	1.67%	3.36%	1.67%	3.36%
Maximum amount outstanding during the quarter	$ 1,105,000	$ 1,015,000	$ 1,175,000	$ 1,015,000
Average amount outstanding during the quarter	1,059,130	1,004,348	1,109,978	985,954
Facility fees	$ 90	$ 45	$ 94	$ 107