Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
AOCI Attributable to Parent, Net of Tax
Beginning balance	$ 934,389	$ 932,264
Other comprehensive (loss) income before reclassifications	(70)	261
Reclassification adjustment for gains included in net loss	0	106
Ending balance	790,244	934,389
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax
Beginning balance	(3,838)	(4,205)
Ending balance	$ (3,908)	$ (3,838)