Fair Value of Financial Instruments - Carrying amount and fair value of financial assets and liabilities (Details) - Fair value of assets and liabilities that are not measured on a recurring basis - USD ($) $ in Thousands	Dec. 31, 2015	Mar. 31, 2015
Carrying Amount
Assets and liabilities that are not measured on a recurring basis
Fixed rate debt	$ 700,000	$ 300,000
Variable rate debt	790,000	1,288,501
Fair Value
Assets and liabilities that are not measured on a recurring basis
Fixed rate debt	712,500	306,000
Variable rate debt	$ 787,697	$ 1,283,539