Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	[1]	Dec. 31, 2016	[1]
Revenues:
Total revenues		$ 2,608,816	$ 1,918,494		$ 1,390,985
Cost of revenues:
Total cost of revenues	[2]	622,658	499,862		398,995
Gross profit		1,986,158	1,418,632		991,990
Operating expenses:
Sales and marketing	[2]	1,203,056	894,977		659,983
Research and development	[2]	529,501	377,518		285,239
General and administrative	[2]	296,027	210,533		158,936
Legal settlements	[2]	0	0		270,000
Total operating expenses	[2]	2,028,584	1,483,028		1,374,158
Loss from operations		(42,426)	(64,396)		(382,168)
Interest expense		(52,733)	(53,394)		(33,278)
Interest income and other income (expense), net		56,135	4,384		5,027
Loss before income taxes		(39,024)	(113,406)		(410,419)
Provision for (benefit from) income taxes		(12,320)	3,440		3,830
Net loss		$ (26,704)	$ (116,846)	[3]	$ (414,249)	[3]
Net loss per share - basic and diluted (in USD per share)		$ (0.15)	$ (0.68)		$ (2.52)
Weighted-average shares used to compute net loss per share - basic and diluted (in shares)		177,846,023	171,175,577		164,533,823
Other comprehensive income (loss):
Foreign currency translation adjustments		$ (1,903)	$ 23,064		$ (6,487)
Unrealized gains (losses) on investments, net of tax		(665)	5,376		588
Other comprehensive income (loss)		(2,568)	28,440		(5,899)
Comprehensive loss		(29,272)	(88,406)		(420,148)
Subscription
Revenues:
Total revenues		2,421,313	1,739,500		1,234,070
Cost of revenues:
Total cost of revenues	[2]	417,421	315,570		235,414
Professional services and other
Revenues:
Total revenues		187,503	178,994		156,915
Cost of revenues:
Total cost of revenues	[2]	$ 205,237	$ 184,292		$ 163,581

[1] As adjusted to reflect the impact of the full retrospective adoption of Topic 606.

[2] Includes stock-based compensation as follows:   Year Ended December 31,   2018   2017   2016       *As Adjusted   *As Adjusted Cost of revenues:           Subscription $ 48,738
  $ 35,334
  $ 28,420
Professional services and other 32,816
  27,401
  26,516
Sales and marketing 228,045
  170,527
  131,571
Research and development 135,203
  92,025
  81,731
General and administrative 99,151
  68,717
  49,416

[3] As adjusted to reflect the impact of the full retrospective adoption of Topic 606.