Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Revenue	$ 291,047	$ 303,612	$ 571,653	$ 622,182
Cost of services	112,607	110,605	210,767	228,581
Gross profit	178,440	193,007	360,886	393,601
Operating expenses:
Sales and marketing	87,394	79,105	163,934	168,397
General and administrative	33,100	44,194	74,379	93,756
Impairment charges	3,611	18,132	3,611	18,230
Total operating expenses	124,105	141,431	241,924	280,383
Operating income	54,335	51,576	118,962	113,218
Other income (expense):
Interest expense	(14,502)	(13,426)	(26,109)	(28,206)
Interest expense, related party	(4,668)	(4,586)	(8,733)	(9,736)
Other components of net periodic pension benefit (cost)	272	(936)	725	(1,137)
Other expense	(2,966)	0	(4,059)	0
Income before (provision) for income taxes	32,471	32,628	80,786	74,139
(Provision) for income taxes	(8,112)	(21,164)	(19,921)	(34,573)
Net income	$ 24,359	$ 11,464	$ 60,865	$ 39,566
Net income per common share:
Basic (in USD per share)	$ 0.72	$ 0.36	$ 1.82	$ 1.24
Diluted (in USD per share)	$ 0.66	$ 0.34	$ 1.72	$ 1.15
Weighted-average shares used in computing basic and diluted net income per common share:
Basic (in shares)	33,622,666	31,435,941	33,367,734	32,007,114
Diluted (in shares)	36,687,030	33,803,465	35,352,445	34,414,996