Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Income Statement [Abstract]
Revenue	$ 333,995	$ 291,047	$ 642,370	$ 571,653
Cost of services	106,013	112,607	216,532	210,767
Gross profit	227,982	178,440	425,838	360,886
Operating expenses:
Sales and marketing	91,813	87,394	185,768	163,934
General and administrative	52,650	33,100	104,844	74,379
Impairment charges	222	3,611	222	3,611
Total operating expenses	144,685	124,105	290,834	241,924
Operating income	83,297	54,335	135,004	118,962
Other income (expense):
Interest expense	(13,756)	(14,502)	(26,864)	(26,109)
Interest expense, related party	(896)	(4,668)	(2,655)	(8,733)
Other components of net periodic pension benefit	9,153	272	9,223	725
Other income (expense)	2,404	(2,966)	8,626	(4,059)
Income before income tax expense	80,202	32,471	123,334	80,786
Income tax expense	(22,200)	(8,112)	(31,821)	(19,921)
Net income	58,002	24,359	91,513	60,865
Other comprehensive income (loss):
Foreign currency translation adjustment	(10,139)	(1,478)	(4,691)	(4,445)
Comprehensive income	$ 47,863	$ 22,881	$ 86,822	$ 56,420
Net income per common share:
Basic (in dollars per share)	$ 1.69	$ 0.72	$ 2.68	$ 1.82
Diluted (in dollars per share)	$ 1.61	$ 0.66	$ 2.47	$ 1.72
Weighted-average shares used in computing basic and diluted net income per common share:
Basic (in shares)	34,250,706	33,622,666	34,205,593	33,367,734
Diluted (in shares)	36,137,989	36,687,030	37,048,087	35,352,445