Derivative Financial Instruments - Impact of Derivatives on the Statements of Changes in Stockholder's Equity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Amount of loss recognized in other comprehensive income (loss)	$ 8,008	$ (3,901)	$ (26,699)
Amount of loss reclassified in interest expense	(11,187)	(17,665)	(21,475)
Total change in other comprehensive income (loss) for unrealized gains (losses) on derivatives, before income tax (expense) benefit	$ 19,195	$ 13,764	$ (5,224)