Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
AOCI Attributable to Parent, Net of Tax
Beginning balance			$ 934,389
Other comprehensive (loss) income before reclassifications	$ (4)	$ (336)	201	$ 811
Ending balance	800,307		800,307
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax
Beginning balance	(3,633)	(3,058)	(3,838)	(4,205)
Ending balance	$ (3,637)	$ (3,394)	$ (3,637)	$ (3,394)