Accumulated Other Comprehensive Income (Loss) - Roll Forward (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Rollforward of Accumulated other comprehensive income (loss)
Beginning balance	$ 924,366	$ 1,081,796	$ 975,060	$ 947,994	$ 1,081,796	$ 947,994
Other comprehensive income before reclassifications, net of tax	1,598		(1,606)		5,118	1,205
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	(2,216)		(602)		(4,405)	(1,152)
Net current-period other comprehensive income (loss)	(618)	1,331	(2,208)	2,261	713	53
Ending balance	825,933	924,366	1,006,690	975,060	825,933	1,006,690
Foreign Currency Derivatives
Rollforward of Accumulated other comprehensive income (loss)
Beginning balance	3,685	3,341	4,462	3,317	3,341	3,317
Other comprehensive income before reclassifications, net of tax	244		(2,323)		3,523	18
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	(2,663)		(1,323)		(5,598)	(2,519)
Net current-period other comprehensive income (loss)	(2,419)		(3,646)		(2,075)	(2,501)
Ending balance	1,266	3,685	816	4,462	1,266	816
Defined Benefit Plan Items
Rollforward of Accumulated other comprehensive income (loss)
Beginning balance	(107,430)	(108,028)	(95,279)	(95,855)	(108,028)	(95,855)
Other comprehensive income before reclassifications, net of tax	0		0		(138)	(143)
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	736		669		1,472	1,388
Net current-period other comprehensive income (loss)	736		669		1,334	1,245
Ending balance	(106,694)	(107,430)	(94,610)	(95,279)	(106,694)	(94,610)
Short-Term Investments
Rollforward of Accumulated other comprehensive income (loss)
Beginning balance	1,193	804	(62)	(602)	804	(602)
Other comprehensive income before reclassifications, net of tax	1,354		717		1,733	1,330
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	(289)		52		(279)	(21)
Net current-period other comprehensive income (loss)	1,065		769		1,454	1,309
Ending balance	2,258	1,193	707	(62)	2,258	707
Total
Rollforward of Accumulated other comprehensive income (loss)
Beginning balance	(102,552)	(103,883)	(90,879)	(93,140)	(103,883)	(93,140)
Net current-period other comprehensive income (loss)	(618)	1,331	(2,208)	2,261
Ending balance	$ (103,170)	$ (102,552)	$ (93,087)	$ (90,879)	$ (103,170)	$ (93,087)