Segment Information - Segment Reconciliation of Operating Income to Net Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Total Segment Adjusted EBITDA	$ 371,839	$ 481,099	$ 586,505
Interest expense	(68,539)	(92,951)	(82,697)
Depreciation and amortization	(146,523)	(206,270)	(266,975)
Other components of net periodic pension cost	(42,236)	(53,161)	(516)
Loss on early extinguishment of debt	0	(6,375)	(18,375)
Adjustments for acquisition accounting, fresh start accounting, and other one-time adjustments including accounting conformity adjustments	0	0	(28,587)
Impairment charges	(24,911)	(5,670)	0
Restructuring and integration expenses	(28,459)	(40,290)	(87,307)
Transaction costs	(20,999)	(6,081)	0
Stock-based compensation (benefit) expense	2,895	(14,119)	(39,604)
Non-cash loss (gain) from remeasurement of indemnification asset	(5,443)	(4,093)	9,518
Other	3,614	943	(10,991)
Income before benefit (provision) for income taxes	41,238	53,566	60,758
Severance costs	11,700
COVID-19 Terminations
Segment Reporting Information [Line Items]
Severance costs	5,000
Impact of ASC 842
Segment Reporting Information [Line Items]
Total Segment Adjusted EBITDA	0	534	0
Impact of ASC 606
Segment Reporting Information [Line Items]
Total Segment Adjusted EBITDA	$ 0	$ 0	$ (213)