Consolidated Statements of Operations and Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Income Statement [Abstract]
Revenue	$ 308,375	$ 280,606
Cost of services	110,519	98,160
Gross profit	197,856	182,446
Operating expenses:
Sales and marketing	93,955	76,540
General and administrative	52,194	41,279
Total operating expenses	146,149	117,819
Operating income	51,707	64,627
Other income (expense):
Interest expense	(13,108)	(11,607)
Interest expense, related party	(1,759)	(4,065)
Other components of net periodic pension benefit (cost)	70	453
Other income (expense), net	6,222	(1,093)
Income before income tax expense	43,132	48,315
Income tax expense	(9,621)	(11,809)
Net income	33,511	36,506
Other comprehensive income (loss):
Foreign currency translation adjustment	5,448	(2,967)
Comprehensive income	$ 38,959	$ 33,539
Net income per common share:
Basic (in dollars per share)	$ 0.98	$ 1.10
Diluted (in dollars per share)	$ 0.88	$ 1.07
Weighted-average shares used in computing basic and diluted net income per common share:
Basic (in shares)	34,159,979	33,108,422
Diluted (in shares)	37,957,685	34,013,480