Accumulated Other Comprehensive Income (Loss) - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands		3 Months Ended	6 Months Ended
		Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance		$ 442,937	$ 450,555	$ 442,937
Ending Balance		429,479	503,655	436,181
Cumulative Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance		(12,026)	(36,332)	(12,026)
Other comprehensive income (loss) before reclassifications			9,097	(11,204)
Net other comprehensive income (loss)			9,097	(11,204)
Ending Balance			(27,235)	(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)	(11,643)	(11,158)
Amounts reclassified from AOCI, net of tax			148	669
Net other comprehensive income (loss)			148	669
Ending Balance			(11,495)	(10,489)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance		(22,568)	(47,975)	(22,568)
Other comprehensive income (loss) before reclassifications			9,097	(11,204)
Amounts reclassified from AOCI, net of tax			148	669
Net other comprehensive income (loss)			9,245	(10,535)
Ending Balance		(25,848)	$ (38,730)	(33,719)
Accumulated Other Comprehensive Income (Loss) | ASU 2016-01
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Adoption of ASU		(616)		(616)	[1]
Unrealized Gains on Investments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance		$ 616		616
Unrealized Gains on Investments | ASU 2016-01
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Adoption of ASU	[1]			$ (616)

[1] ^{Upon the adoption of ASU 2016-01, Financial Instruments – Overall: Recognition and Measurement of Financial Assets and Financial Liabilities, we recorded a cumulative-effect adjustment from unrealized gains on investments to beginning retained earnings.}