Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Mar. 31, 2015
Prepaid expenses and other current assets
Derivative assets (liabilities)
Net asset	$ 39,500
Accrued expenses and other payables
Derivative assets (liabilities)
Net asset	26,700
Commodity contracts
Derivative assets (liabilities)
Net asset	12,778	$ 32,328
Commodity contracts | Prepaid expenses and other current assets
Derivative assets (liabilities)
Net asset	40,099	60,278
Commodity contracts | Accrued expenses and other payables
Derivative assets (liabilities)
Net asset	(27,321)	(27,950)
Recurring | Commodity contracts
Assets:
Derivative Assets	42,890	118,742
Netting of counterparty contracts, assets	(2,791)	(1,804)
Cash collateral provided (held), assets		(56,660)
Liabilities:
Derivative Liabilities	38,655	32,733
Netting of counterparty contracts, liabilities	2,791	1,804
Derivative, Collateral, Right to Reclaim Cash	8,543	2,979
Commodity derivatives reported on consolidated balance sheet, assets	40,099	60,278
Commodity derivatives reported on consolidated balance sheet, liabilities	27,321	27,950
Recurring | Level 1 | Commodity contracts
Assets:
Derivative Assets	2,879	83,779
Liabilities:
Derivative Liabilities	9,070	3,969
Recurring | Level 2 | Commodity contracts
Assets:
Derivative Assets	40,011	34,963
Liabilities:
Derivative Liabilities	$ 29,585	$ 28,764