Accumulated Other Comprehensive Loss - Amounts Included in Accumulated Other Comprehensive Loss, Net of Tax (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			$ 1,252,873
Other comprehensive loss before reclassifications			(7,219)
Amounts reclassified from accumulated other comprehensive loss			4,739
Other comprehensive income (loss)	$ 28,373	$ 337	(2,480)	$ (37,618)
Ending balance	1,388,580	1,089,694	1,388,580	1,089,694
Accumulated Other Comprehensive Loss
Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(291,806)	(297,697)	(260,953)	(259,742)
Ending balance	(263,433)	$ (297,360)	(263,433)	$ (297,360)
Unrecognized Net Defined Benefit Plan Costs
Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			(168,604)
Other comprehensive loss before reclassifications			0
Amounts reclassified from accumulated other comprehensive loss			3,754
Other comprehensive income (loss)			3,754
Ending balance	(164,850)		(164,850)
Change in Fair Value of Derivatives
Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			(4,656)
Other comprehensive loss before reclassifications			484
Amounts reclassified from accumulated other comprehensive loss			985
Other comprehensive income (loss)			1,469
Ending balance	(3,187)		(3,187)
Foreign Currency Translation
Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			(87,693)
Other comprehensive loss before reclassifications			(7,703)
Amounts reclassified from accumulated other comprehensive loss			0
Other comprehensive income (loss)			(7,703)
Ending balance	$ (95,396)		$ (95,396)