Interest on Borrowings (Components of interest expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Interest expense, borrowings:
Interest expense	$ 125,412	$ 106,221	$ 85,404
Capitalized interest	(6,466)	(4,863)	(3,623)
Amortization of transaction costs	3,867	3,445	3,235
Interest expense resulting from derivatives	3,893	8,603	12,699
Total interest expense	126,706	113,406	97,715
Amortization on early extinguishment of debt		499
Total	$ 126,706	$ 113,905	$ 97,715