Fair Value Measurements - Summary of Changes of Derivative Commodity Instruments in Fair Value (Details) - Derivative Commodity Instruments - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ (10,650)	$ (14,063)	$ (16,059)	$ 24,436
Realized gains (losses)	(4,610)	(2,820)	(11,526)	10,994
Unrealized gains (losses) relating to instruments held at the reporting date	6,353	(3,569)	11,762	(42,068)
Settlements during period	4,610	2,820	11,526	(10,994)
Balance at end of period	(4,297)	(17,632)	(4,297)	(17,632)
Mark-to-market loss included in earnings	$ 1,500	$ (5,400)	$ (1,600)	$ (20,200)