Income Taxes Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 274,116	$ 116,190	$ 56,138
Accrued and prepaid expenses	11,828	11,594	9,140
Stock-based compensation	35,035	11,147	7,131
Research and development credits	65,955	32,206	16,212
Charitable contributions	3,172	3,100	1,233
Capped call	9,914	13,175	0
Debt issuance cost	493	638	0
Depreciable property	2	0	0
Lease liability	39,117
Other	0	194	472
Gross deferred tax assets	439,632	188,244	90,326
Valuation allowance	(255,893)	(147,354)	(78,900)
Net deferred tax assets	183,739	40,890	11,426
Capitalized software	(13,032)	(10,686)	(7,664)
Prepaid expenses	(1,157)	(838)	(1,015)
Acquired intangibles	(107,281)	(2,997)	(2,101)
Property and equipment	(1,578)	(1,990)	(2,380)
Convertible debt	(20,745)	(27,164)	0
Right-of-use asset	(39,630)
Deferred commissions	(7,446)	(2,396)	(718)
Other	(405)	0	0
Net deferred tax liability	$ (7,535)	$ (5,181)	$ (2,452)