Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Revenue	$ 240,325	$ 319,116	$ 862,507	$ 1,076,244
Operating expenses:
Cost of services (exclusive of depreciation and amortization)	87,347	109,588	278,941	364,873
Sales and marketing	60,775	83,730	201,939	266,643
General and administrative	34,176	34,352	116,723	130,727
Depreciation and amortization	35,454	50,471	110,883	155,285
Impairment charges	1,184	60	19,414	5,059
Total operating expenses	218,936	278,201	727,900	922,587
Operating income	21,389	40,915	134,607	153,657
Other income (expense):
Interest expense	(11,442)	(17,464)	(39,648)	(51,998)
Interest expense, related party	(4,167)	(6,202)	(13,903)	(19,070)
Other components of net periodic pension cost	(30,175)	(16,111)	(31,312)	(19,797)
Loss on early extinguishment of debt	0	0	0	(6,375)
(Loss) income before benefit (provision) for income taxes	(24,395)	1,138	49,744	56,417
Benefit (provision) for income taxes	24,250	(1,410)	(10,323)	(18,860)
Net (loss) income	$ (145)	$ (272)	$ 39,421	$ 37,557
Net (loss) income per common share:
Basic (in USD per share)	$ 0	$ (0.01)	$ 1.25	$ 0.87
Diluted (in USD per share)	$ 0	$ (0.01)	$ 1.16	$ 0.82
Weighted-average shares used in computing basic and diluted net (loss) income per common share:
Basic (in shares)	30,857,617	33,468,556	31,621,039	43,323,602
Diluted (in shares)	30,857,617	33,468,556	33,990,771	46,028,655