Components of Interest Expense (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Interest expense, borrowings:
Interest expense	$ 16,529	$ 16,040	$ 32,175	$ 31,879
Capitalized interest	(94)	(46)	(171)	(78)
Amortization of transaction costs	1,050	1,058	2,135	2,094
Interest expense resulting from derivatives	4,628	5,911	11,465	11,701
Total interest expense	$ 22,113	$ 22,963	$ 45,604	$ 45,596