Fair Value Measurements - Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Current derivative asset		$ 12,728	$ 16,865
Long-term derivative asset	[1]	1,454
Total derivative instruments		14,182
Current derivative liability		61,926
Long-term derivative liability	[2]	7,847
Total derivative instruments		69,773
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Current derivative asset		12,728
Long-term derivative asset	[1]	1,454
Total derivative instruments		14,182
Current derivative liability		61,926
Long-term derivative liability	[2]	7,847
Total derivative instruments		$ 69,773

[1] Included in Other assets in the Condensed Consolidated Balance Sheet.

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