Fair Value Measurements - Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Current derivative asset		$ 25,118	$ 16,865
Long-term derivative asset	[1]	7,697
Total derivative instruments		32,815
Current derivative liability		21,036
Long-term derivative liability	[2]	2,418
Total derivative instruments		23,454
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Current derivative asset		25,118
Long-term derivative asset	[1]	7,697
Total derivative instruments		32,815
Current derivative liability		21,036
Long-term derivative liability	[2]	2,418
Total derivative instruments		$ 23,454

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

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