Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive loss at beginning of period			$ 876,589
Accumulated other comprehensive loss at end of period	$ 907,506		907,506
Gains and Losses on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive loss at beginning of period	(23)	$ (95)	(69)	$ (133)
Losses reclassified from net accumulated other comprehensive loss	23	19	69	57
Net current period other comprehensive income	23	19	69	57
Accumulated other comprehensive loss at end of period	$ 0	$ (76)	$ 0	$ (76)