Selected Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Revenue	$ 595,726		$ 563,309		$ 519,845		$ 472,489		$ 467,867		$ 437,633		$ 405,211		$ 335,475		$ 2,151,369	$ 1,646,186	$ 1,129,167
Total cost of revenue	220,734		201,726		185,962		169,570		160,702		157,016		145,434		121,265		777,992	584,417	406,051
Gross profit	374,992		361,583		333,883		302,919		307,165		280,617		259,777		214,210		1,373,377	1,061,769	723,116
Operating expenses:
Research and development	118,439		117,589		104,078		102,362		107,180		79,610		81,194		81,610		442,468	349,594	273,581
Sales and marketing	50,911		47,903		46,188		42,140		38,808		40,640		38,630		37,027		187,142	155,105	130,887
General and administrative	12,000		15,321		18,420		19,679		21,789		19,535		23,319		22,155		65,420	86,798	75,239
Legal settlement	0		0		405,000	[1]	0		0		0		0		0		405,000	0	0
Total operating expenses	181,350		180,813		573,686		164,181		167,777		139,785		143,143		140,792		1,100,030	591,497	479,707
Income from operations	193,642		180,770		(239,803)		138,738		139,388		140,832		116,634		73,418		273,347	470,272	243,409
Other income (expense), net:
Interest expense	(661)		(673)		(680)		(687)		(741)		(701)		(623)		(715)
Other income (expense), net	5,509		9,292		(1,489)		4,843		2,988		2,136		1,119		1,025		18,155	7,268	1,952
Total other income (expense), net	4,848		8,619		(2,169)		4,156		2,247		1,435		496		310		15,454	4,488	(1,184)
Income before income taxes	198,490		189,389		(241,972)		142,894		141,635		142,267		117,130		73,728		288,801	474,760	242,225
Provision for (benefit from) income taxes	28,168	[2]	20,865	[2]	(86,703)	[2]	(1,644)	[2]	37,802	[2]	8,545	[2]	14,445	[2]	(9,233)	[2]	(39,314)	51,559	58,036
Net income	$ 170,322		$ 168,524		$ (155,269)		$ 144,538		$ 103,833		$ 133,722		$ 102,685		$ 82,961		$ 328,115	$ 423,201	$ 184,189
Net income attributable to common stockholders:
Basic (in dollars per share)	$ 2.26		$ 2.25		$ (2.08)		$ 1.95		$ 1.42		$ 1.84		$ 1.42		$ 1.16		$ 4.39	$ 5.85	$ 2.66
Diluted (in dollars per share)	$ 2.10		$ 2.08		$ (2.08)		$ 1.79		$ 1.29		$ 1.68		$ 1.30		$ 1.07		$ 4.06	$ 5.35	$ 2.50
Excess tax benefits included in income taxes	$ 7,800		$ 22,300		$ 20,100		$ 25,300		$ 38,300		$ 23,800		$ 19,100		$ 28,800		$ 75,500	$ 110,000
Provisional amount in connection with the Tax Act									51,800
Product
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Revenue	503,235		485,481		444,767		407,617		407,195		380,344		353,904		291,367		1,841,100	1,432,810	$ 991,337
Total cost of revenue	204,507		187,764		171,622		156,691		147,919		145,874		134,406		109,836		720,584	538,035	369,768
Service
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Revenue	92,491		77,828		75,078		64,872		60,672		57,289		51,307		44,108		310,269	213,376	137,830
Total cost of revenue	$ 16,227		$ 13,962		14,340		$ 12,879		$ 12,783		$ 11,142		$ 11,028		$ 11,429		57,408	$ 46,382	$ 36,283
Cisco Lawsuits
Operating expenses:
Legal settlement					405,000
Other income (expense), net:
Provision for (benefit from) income taxes					$ (99,000)												$ (96,900)

[1] See Note 14.

[2] Resulting from the adoption of ASU 2016-09, provision for (benefit from) income taxes for the first, second, third and fourth quarter of 2018 included excess tax benefits of $25.3 million, $20.1 million, $22.3 million and $7.8 million, respectively, of 2017 included $28.8 million, $19.1 million, $23.8 million and $38.3 million, respectively. In addition, provision for income taxes for the fourth quarter of 2017 included a provisional amount of $51.8 million in connection with the Tax Act enacted on December 22, 2017. See Note 10 for details. Benefit from income taxes for the second quarter of 2018 also included a benefit of $99.0 million in connection with our legal settlement with Cisco. See Note 14.