Interest on Borrowings (Interest Rates and Company Borrowings) (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Interest and debt expense:
Weighted average interest rate during the year	3.31%	3.39%	2.48%
Interest rate at year end	2.86%	3.60%	2.84%
Maximum amount outstanding during the year	$ 1,086,000	$ 959,400	$ 538,000
Average amount outstanding during the year	1,002,081	699,415	517,997
Facility fees	$ 193	$ 374	$ 410