Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Revenue	$ 280,606	$ 318,570
Cost of services	98,160	117,976
Gross profit	182,446	200,594
Operating expenses:
Sales and marketing	76,540	89,292
General and administrative	41,279	49,562
Impairment charges	0	98
Total operating expenses	117,819	138,952
Operating income	64,627	61,642
Other income (expense):
Interest expense	(11,607)	(14,780)
Interest expense, related party	(4,065)	(5,150)
Other components of net periodic pension cost	453	(201)
Other expense	(1,093)	0
Income before (provision) for income taxes	48,315	41,511
(Provision) for income taxes	11,809	13,409
Net income	$ 36,506	$ 28,102
Net income per common share:
Basic (in USD per share)	$ 1.10	$ 0.86
Diluted (in USD per share)	$ 1.07	$ 0.80
Weighted-average shares used in computing basic and diluted net income per common share:
Basic (in shares)	33,108,422	32,578,286
Diluted (in shares)	34,013,480	35,026,526