Fair Value Measurements - Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Current derivative asset		$ 14,480	$ 16,865
Long-term derivative asset	[1]	3,692
Total derivative instruments		18,172
Current derivative liability		54,891
Long-term derivative liability	[2]	7,853
Total derivative instruments		62,744
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Current derivative asset		14,480
Long-term derivative asset	[1]	3,692
Total derivative instruments		18,172
Current derivative liability		54,891
Long-term derivative liability	[2]	7,853
Total derivative instruments		$ 62,744

[1] Included in other assets in the Consolidated Balance Sheet.

[2] Included in other long-term obligations in the Consolidated Balance Sheet.