Fair Value Measurements - Derivative Instrument Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, at fair value	$ 788,366	$ 481,654
Fair value on a recurring basis | Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, at fair value	204,161	112,107
Liability derivative instruments, at fair value	156,272	126,582
Fair value on a recurring basis | Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, at fair value	584,205	369,547
Liability derivative instruments, at fair value	222,562	209,469
Fair value on a recurring basis | Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, at fair value	0	0
Liability derivative instruments, at fair value	0	0
Fair value on a recurring basis | Fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, at fair value	788,366	481,654
Liability derivative instruments, at fair value	$ 378,834	$ 336,051