Stockholders' Equity - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	$ 442,937	[1]
Ending Balance	478,064
Unrealized Gains on Investments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	616
Adoption of ASU 2016-01	(616)	[2]
Net other comprehensive income (loss)	(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	(7,864)
Net other comprehensive income (loss)	(7,864)
Ending Balance	(19,890)
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	(715)
Net other comprehensive income (loss)	(715)
Ending Balance	(11,873)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(22,568)
Adoption of ASU 2016-01	(616)	[2]
Other comprehensive income before reclassifications	(7,864)
Amounts reclassified from AOCI, net of tax	(715)
Net other comprehensive income (loss)	(9,195)
Ending Balance	$ (31,763)

[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.

[2] Upon the adoption of ASU 2016-01, we recorded a cumulative-effect adjustment from unrealized gains on investments to beginning retained earnings.