Derivative Financial Instruments - Impact of Derivatives on Consolidated Statement of Changes in Stockholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Amount of gain recognized in other comprehensive income (loss)	$ 9,471	$ (4,698)	$ 28,200	$ (3,258)
Less: amount of loss reclassified in interest expense	(543)	(2,669)	(2,104)	(6,008)
Total change in other comprehensive income (loss) for unrealized gains (losses) on derivatives, before income tax (expense) benefit	$ 10,014	$ (2,029)	$ 30,304	$ 2,750