Stockholders' Equity - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	$ 442,937	[1]
Ending Balance	436,181
Unrealized Gains on Investments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	616
Net other comprehensive income (loss)	(616)
Adoption of ASU 2016-01	(616)
Cumulative Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(12,026)
Other comprehensive income before reclassifications	(11,204)
Net other comprehensive income (loss)	(11,204)
Ending Balance	(23,230)
Unrecognized Net Actuarial Loss and Prior Service Credit, Net
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(11,158)
Amounts reclassified from AOCI, net of tax	669
Net other comprehensive income (loss)	669
Ending Balance	(10,489)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(22,568)
Other comprehensive income before reclassifications	(11,204)
Amounts reclassified from AOCI, net of tax	669
Net other comprehensive income (loss)	(11,151)
Ending Balance	(33,719)
Adoption of ASU 2016-01	$ (616)

[1] We determined that the cumulative effect of initially applying Topic 606 as an adjustment to the opening balance of retained earnings was not material, and therefore we made no adjustment.