Consolidated Statements of Operations and Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Revenue	$ 1,113,382	$ 1,109,435	$ 1,421,374
Cost of services	408,043	439,742	581,293
Gross profit	705,339	669,693	840,081
Operating expenses:
Sales and marketing	357,813	315,195	431,815
General and administrative	153,902	177,574	196,543
Impairment charges	3,611	24,911	5,670
Total operating expenses	515,326	517,680	634,028
Operating income	190,013	152,013	206,053
Other income (expense):
Interest expense	(48,867)	(51,537)	(68,181)
Interest expense, related party	(17,507)	(17,002)	(24,770)
Other components of net periodic pension benefit (cost)	14,829	(42,236)	(53,161)
Other expense	(4,154)	0	(6,375)
Income before income tax (expense) benefit	134,314	41,238	53,566
Income tax (expense) benefit	(32,737)	107,983	(18,062)
Net income	101,577	149,221	35,504
Other comprehensive income (loss):
Foreign currency translation adjustment	(8,047)	0	0
Comprehensive income	$ 93,530	$ 149,221	$ 35,504
Net income per common share:
Basic (in USD per share)	$ 3.02	$ 4.73	$ 0.87
Diluted (in USD per share)	$ 2.78	$ 4.42	$ 0.82
Weighted-average shares used in computing basic and diluted net income per common share:
Basic (in shares)	33,607,446	31,522,845	40,845,128
Diluted (in shares)	36,495,746	33,795,594	43,465,998