Comprehensive Income and Accumulated Other Comprehensive Income (Loss) - Summary of Effects of Reclassifications from Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Amortization of pension and other postretirement benefit plan items:
Total before tax	$ 66,127	$ 152,410	$ 230,080
Tax benefit	11,724	42,519	62,936
Total net of tax	(55,162)	$ (377,015)	$ 160,894
Settlement loss
Amortization of pension and other postretirement benefit plan items:
Other nonoperating expense (income)	3,153
Amount Reclassified from Accumulated Other Comprehensive Income (Loss) | Actuarial losses
Amortization of pension and other postretirement benefit plan items:
Other nonoperating expense (income)	2,871
Amount Reclassified from Accumulated Other Comprehensive Income (Loss) | Actuarial losses | Grass Valley
Amortization of pension and other postretirement benefit plan items:
Other nonoperating expense (income)	771
Amount Reclassified from Accumulated Other Comprehensive Income (Loss) | Prior service cost
Amortization of pension and other postretirement benefit plan items:
Other nonoperating expense (income)	190
Amount Reclassified from Accumulated Other Comprehensive Income (Loss) | Pension and Other Postretirement Benefit Plans
Amortization of pension and other postretirement benefit plan items:
Total before tax	6,985
Tax benefit	(1,662)
Total net of tax	5,323
Amount Reclassified from Accumulated Other Comprehensive Income (Loss) | Foreign Currency Translation Component | Grass Valley
Amortization of pension and other postretirement benefit plan items:
Other nonoperating expense (income)	$ (10,100)