Income Taxes - Components of Net Deferred Tax Balances (Details) - USD ($) $ in Thousands	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017
Deferred tax assets
Net operating loss carryforwards	$ 423,379	$ 280,835
Accruals and reserves	5,668	3,180
Stock-based compensation	33,405	39,334
Operating lease liability	40,495
Research and development credits	39,480	22,876
Other	7,536	10,715
Total deferred tax assets	549,963	356,940
Deferred tax liabilities
Operating lease right-of-use asset	(32,736)
Deferred contract acquisition costs	(36,567)	(28,103)
Convertible debt	(24,737)	(29,531)
Acquired intangibles	(13,493)	(16,766)
Other	(1,457)	(3,885)
Total deferred tax liabilities	(108,990)	(78,285)
Less: Valuation allowance	(445,746)	(282,141)	$ (119,153)	$ (133,029)
Net deferred tax liabilities	$ (4,773)	$ (3,486)