Long-term Debt - Discounted Carrying Values (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Aug. 31, 2016	Mar. 31, 2016	Sep. 30, 2015	Mar. 31, 2015	Dec. 31, 2013
Long-term debt
Debt instrument, face amount	$ 768,800			$ 573,900
Carrying amount of long-term debt, net of discounts and debt issue costs	754,501			562,330
Less current portion	(7,785)			(4,250)
Long-term debt	746,716			558,080
Senior secured term loan, due March 2022
Long-term debt
Debt instrument, face amount	768,804			423,938	$ 425,000
Carrying amount of long-term debt, net of discounts and debt issue costs	$ 754,501			414,490
7.25% Senior notes, due January 2019
Long-term debt
Debt instrument, face amount				150,000		$ 150,000
Carrying amount of long-term debt, net of discounts and debt issue costs				$ 147,840
Interest rate on long-term debt (as a percent)	7.25%	7.25%	7.25%	7.25%		7.25%