Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (177,602)	$ (245,066)	$ (213,752)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	61,744	50,203	32,254
Stock-based compensation expense	150,673	116,668	58,225
Contribution of common stock to the Pure Good Foundation	0	0	11,900
Other	2,054	1,584	(1,093)
Changes in operating assets and liabilities:
Accounts receivable, net	(74,505)	(44,049)	(67,292)
Inventory	(12,595)	(3,776)	1,481
Deferred commissions	(11,997)	(740)	(13,021)
Prepaid expenses and other assets	(23,799)	(6,133)	(8,704)
Accounts payable	29,278	10,644	24,901
Accrued compensation and other liabilities	26,622	19,381	24,710
Deferred revenue	102,883	86,922	142,535
Net cash provided by (used in) operating activities	72,756	(14,362)	(7,856)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchases of property and equipment	(65,060)	(76,773)	(39,355)
Purchase of intangible assets	0	(1,000)	0
Purchases of marketable securities	(202,656)	(526,717)	0
Sales of marketable securities	66,489	114,354	0
Maturities of marketable securities	144,068	48,513	0
Net increase in restricted cash	(2,029)	(5,600)	(2,485)
Net cash used in investing activities	(59,188)	(447,223)	(41,840)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from initial public offering, net of issuance costs	0	0	459,425
Net proceeds from exercise of stock options	24,677	14,912	6,008
Proceeds from issuance of common stock under employee stock purchase plan	22,137	25,606	0
Payments of deferred offering costs	0	0	(3,702)
Net cash provided by financing activities	46,814	40,518	461,731
Net increase (decrease) in cash and cash equivalents	60,382	(421,067)	412,035
Cash and cash equivalents, beginning of period	183,675	604,742	192,707
Cash and cash equivalents, end of period	244,057	183,675	604,742
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Cash paid for income taxes	3,090	2,866	1,118
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING INFORMATION
Conversion of convertible preferred stock to common stock upon initial public offering	0	0	543,940
Property and equipment purchased but not yet paid	9,940	7,414	6,212
Vesting of early exercised stock options	1,042	3,399	1,725
Unpaid deferred offering costs	$ 0	$ 0	$ 546