Segment Information - Segment Reconciliation of Operating Income to Net Income (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Income (loss) before income tax expense (benefit)	$ 49,426,000	$ (24,395,000)	$ 130,212,000	$ 49,744,000
Interest expense	16,546,000	15,609,000	51,388,000	53,551,000
Depreciation and amortization	31,049,000	35,454,000	80,675,000	110,883,000
Other components of net periodic pension benefit (cost)	(273,000)	30,175,000	(998,000)	31,312,000
Loss on termination of leaseback obligations	0	0	3,409,000	0
Impairment charges	0	1,184,000	3,611,000	19,414,000
Restructuring and integration expenses	2,312,000	6,710,000	15,036,000	23,902,000
Transaction costs	3,987,000	4,913,000	19,973,000	14,679,000
Stock compensation expense (benefit)	2,340,000	1,289,000	6,232,000	(4,195,000)
Non-cash (gain) loss from remeasurement of indemnification asset	(404,000)	(540,000)	(1,248,000)	3,878,000
Other	(2,624,000)	(1,105,000)	(4,245,000)	(2,960,000)
Total Segment EBITDA	102,359,000	69,294,000	304,045,000	300,208,000
Severance costs	1,886,000	$ 3,297,000	3,046,000	10,646,000
COVID-19 Terminations
Segment Reporting Information [Line Items]
Severance costs	$ 0		$ 0	$ 5,000,000