Interest on Borrowings (Interest Rates and Company Borrowings) (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Interest and debt expense:
Weighted average interest rate during the year	1.83%	1.67%	1.70%
Interest rate at year end	2.06%	1.82%	1.65%
Maximum amount outstanding during the year	$ 597,000	$ 347,000	$ 232,000
Average amount outstanding during the year	477,888	237,372	187,004
Facility fees	$ 158	$ 201	$ 336