Interest on Borrowings (Interest Rates and Company Borrowings) (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Interest and debt expense:
Weighted average interest rate during the year	3.39%	2.48%	1.83%
Interest rate at year end	3.60%	2.84%	2.06%
Maximum amount outstanding during the year	$ 959,400	$ 538,000	$ 597,000
Average amount outstanding during the year	699,415	517,997	477,888
Facility fees	$ 374	$ 410	$ 158