Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Revenue	$ 297,290	$ 240,325	$ 868,943	$ 862,507
Cost of services	104,167	105,444	314,934	334,025
Gross profit	193,123	134,881	554,009	528,482
Operating expenses:
Sales and marketing	94,343	73,306	258,277	241,703
General and administrative	32,983	39,002	107,362	132,758
Impairment charges	0	1,184	3,611	19,414
Total operating expenses	127,326	113,492	369,250	393,875
Operating income	65,797	21,389	184,759	134,607
Other income (expense):
Interest expense	(12,050)	(11,442)	(38,159)	(39,648)
Interest expense, related party	(4,496)	(4,167)	(13,229)	(13,903)
Other components of net periodic pension benefit (cost)	273	(30,175)	998	(31,312)
Other expense	(98)	0	(4,157)	0
Income (loss) before income tax expense (benefit)	49,426	(24,395)	130,212	49,744
Income tax (expense) benefit	(13,802)	24,250	(33,723)	(10,323)
Net income (loss)	35,624	(145)	96,489	39,421
Other comprehensive income (loss):
Foreign currency translation adjustment	(4,100)	0	(8,545)	0
Comprehensive income (loss)	$ 31,524	$ (145)	$ 87,944	$ 39,421
Net income (loss) per common share:
Basic (in USD per share)	$ 1.05	$ 0	$ 2.87	$ 1.25
Diluted (in USD per share)	$ 0.95	$ 0	$ 2.67	$ 1.16
Weighted-average shares used in computing basic and diluted net income (loss) per common share:
Basic (in shares)	34,013,897	30,857,617	33,585,488	31,621,039
Diluted (in shares)	37,620,116	30,857,617	36,110,702	33,990,771