Stockholders' Equity - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2017 USD ($)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	$ 370,638
Ending Balance	468,494
Unrealized Gains on Investments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	421
Other comprehensive income before reclassifications	188
Amounts reclassified from AOCI, net of tax	(45)
Net other comprehensive income	143
Ending Balance	564
Cumulative Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(29,084)
Other comprehensive income before reclassifications	18,820
Net other comprehensive income	18,820
Ending Balance	(10,264)
Unrecognized Net Actuarial Loss and Prior Service Credit, Net
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(10,728)
Amounts reclassified from AOCI, net of tax	184
Net other comprehensive income	184
Ending Balance	(10,544)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(39,391)
Other comprehensive income before reclassifications	19,008
Amounts reclassified from AOCI, net of tax	139
Net other comprehensive income	19,147
Ending Balance	$ (20,244)