Quarterly Results of Operations - Summary of Quarterly Results of Operations (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Operating revenues	$ 549,842	$ 517,099	$ 498,180	$ 478,423	$ 443,661	$ 425,333	$ 409,616	$ 416,780	$ 2,043,544	$ 1,695,390	$ 1,557,796
Cost of revenues	95,903	89,674	87,327	85,780	75,935	70,704	70,456	74,609
Selling and marketing	68,708	59,819	58,191	56,467	56,662	52,668	51,617	55,549	243,185	216,496	219,298
Research and development	30,819	28,352	27,531	24,862	27,056	24,901	22,534	26,562	111,564	101,053	98,334
General and administrative	44,873	38,110	30,182	34,728	27,872	27,613	28,309	30,833	147,893	114,627	110,093
Amortization of intangible assets	21,023	14,105	30,396	15,068	14,770	14,333	14,062	13,776	80,592	56,941	49,410
Depreciation and amortization of property, equipment and leasehold improvements	7,929	6,809	7,020	7,143	7,281	7,494	7,463	7,567	28,901	29,805	29,999
Total operating expenses	269,255	236,869	240,647	224,048	209,576	197,713	194,441	208,896	970,819	810,626	802,095
Operating income	280,587	280,230	257,533	254,375	234,085	227,620	215,175	207,884	1,072,725	884,764	755,701
Interest income	(368)	(396)	(347)	(386)	(301)	(475)	(771)	(3,483)	(1,497)	(5,030)	(16,403)
Interest expense	40,336	42,137	39,557	37,584	37,330	37,536	41,227	40,231	159,614	156,324	148,041
Other expense (income)	(5,144)	37,839	22,628	1,149	1,890	1,516	35,552	8,287	56,472	47,245	20,745
Other expense (income), net	34,824	79,580	61,838	38,347	38,919	38,577	76,008	45,035	214,589	198,539	152,383
Income before provision for income taxes	245,763	200,650	195,695	216,028	195,166	189,043	139,167	162,849	858,136	686,225	603,318
Provision for income taxes	51,898	30,774	30,272	19,209	38,950	6,685	24,044	14,724	132,153	84,403	39,670
Net income	$ 193,865	$ 169,876	$ 165,423	$ 196,819	$ 156,216	$ 182,358	$ 115,123	$ 148,125	$ 725,983	$ 601,822	$ 563,648
Earnings per basic common share	$ 2.35	$ 2.06	$ 2.01	$ 2.38	$ 1.89	$ 2.18	$ 1.38	$ 1.75	$ 8.80	$ 7.19	$ 6.66
Earnings per diluted common share	$ 2.32	$ 2.03	$ 1.99	$ 2.36	$ 1.87	$ 2.16	$ 1.36	$ 1.73	$ 8.70	$ 7.12	$ 6.59
Weighted average shares outstanding used in computing per share data
Basic	82,473	82,470	82,454	82,640	82,737	83,602	83,666	84,870	82,508	83,716	84,644
Diluted	83,578	83,554	83,295	83,493	83,707	84,479	84,349	85,548	83,479	84,517	85,536