Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 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	$ 894,313		894,313
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	(46)	$ (114)	(69)	$ (133)
Losses reclassified from net accumulated other comprehensive loss	23	19	46	38
Net current period other comprehensive income	23	19	46	38
Accumulated other comprehensive loss at end of period	$ (23)	$ (95)	$ (23)	$ (95)