Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Assets:
Noncurrent derivative instruments	$ 9,534	$ 0
Net Amounts Presented in the Balance Sheets	48,597
Liabilities:
Net Amount Presented in the Balance Sheets	983
Recurring
Assets:
Derivative instruments	39,063	50
Noncurrent derivative instruments	9,534
Net Amounts Presented in the Balance Sheets	48,597
Liabilities:
Derivative instruments	(481)	(65,467)
Noncurrent derivative instruments	(502)	(3,006)
Net Amount Presented in the Balance Sheets	(983)	(68,473)
Net derivative liability	47,614	(68,423)
Recurring | Level 2
Assets:
Derivative instruments	33,437	50
Noncurrent derivative instruments	7,587
Net Amounts Presented in the Balance Sheets	41,024
Liabilities:
Derivative instruments	(481)	(57,927)
Noncurrent derivative instruments	(574)	(1,694)
Net Amount Presented in the Balance Sheets	(1,055)	(59,621)
Net derivative liability	39,969	(59,571)
Recurring | Level 3
Assets:
Derivative instruments	5,626	0
Noncurrent derivative instruments	1,947
Net Amounts Presented in the Balance Sheets	7,573
Liabilities:
Derivative instruments	0	(7,540)
Noncurrent derivative instruments	72	(1,312)
Net Amount Presented in the Balance Sheets	72	(8,852)
Net derivative liability	$ 7,645	$ (8,852)