Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive loss at beginning of period			$ 811,850
Accumulated other comprehensive loss at end of period	$ 833,294		833,294
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	(95)	$ (171)	(133)	$ (209)
Losses reclassified from net accumulated other comprehensive loss	19	19	57	57
Net current period other comprehensive income	19	19	57	57
Accumulated other comprehensive loss at end of period	$ (76)	$ (152)	$ (76)	$ (152)