Interest on Borrowings (Interest Rates and Company Borrowings) (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Interest and debt expense:
Weighted average interest rate during the year	2.48%	1.83%	1.67%
Interest rate at year end	2.84%	2.06%	1.82%
Maximum amount outstanding during the year	$ 538,000	$ 597,000	$ 347,000
Average amount outstanding during the year	517,997	477,888	237,372
Facility fees	$ 410	$ 158	$ 201