Borrowings (Interest Rates and Company Borrowings) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Interest and debt expense:
Weighted average interest rate during the quarter	2.43%	1.73%	2.34%	1.73%
Interest rate at quarter end	2.43%	1.73%	2.43%	1.73%
Maximum amount outstanding during the quarter	$ 538,000	$ 462,000	$ 538,000	$ 462,000
Average amount outstanding during the period	516,946	431,815	508,350	400,896
Facility fees	$ 49	$ 49	$ 125	$ 89