CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018
Cash flows from operating activities
Net loss	$ (175,522)	$ (99,011)	$ (83,973)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	12,783	5,792	3,703
Stock-based compensation	75,776	37,403	21,235
Amortization of debt discount and issuance costs	14,847	7,399	0
Amortization of finance right-of-use assets	3,976	0	0
Amortization of operating right-of-use assets	3,015	0	0
Non-cash interest on finance lease liabilities	1,823	1,570	0
Deferred income taxes	(3,292)	(4,960)	(302)
Accretion of discount on short-term investments	(4,060)	(3,875)	(152)
Change in fair value of warrant liability	0	0	(101)
Loss on early extinguishment of debt	14,522	0	0
Change in operating assets and liabilities, net of the impact from the acquisition:
Accounts receivable, net	(12,692)	(19,445)	(16,095)
Prepaid expenses and other current assets	(3,794)	(1,487)	(2,436)
Deferred commissions	(28,362)	(16,134)	(6,422)
Other long-term assets	(53)	(214)	(687)
Accounts payable	513	(913)	(371)
Deferred rent	0	1,642	(133)
Accrued liabilities	20,439	13,564	8,115
Operating lease liabilities	(3,291)	0	0
Deferred revenue	53,054	36,680	32,738
Other liabilities, non-current	778	0	0
Net cash used in operating activities	(29,540)	(41,989)	(44,881)
Cash flows from investing activities
Purchases of property and equipment	(3,564)	(6,848)	(2,135)
Acquisition, net of cash acquired	(38,629)	(55,517)	0
Proceeds from maturities of marketable securities	470,000	450,000	82,230
Purchases of marketable securities	(429,452)	(547,914)	(252,382)
Net cash used in investing activities	(1,645)	(160,279)	(172,287)
Cash flows from financing activities
Proceeds from exercise of stock options, including early exercised stock options	16,775	22,244	8,367
Proceeds from the issuance of common stock under the Employee Stock Purchase Plan	13,420	10,532	0
Repurchase of early exercised stock options	(43)	(327)	(242)
Principal repayments of finance leases	(1,915)	0	0
Proceeds from borrowings on convertible senior notes, net of issuance costs	1,132,991	291,145	0
Payments for 2024 Notes Partial Repurchase	(479,070)	0	0
Payment for purchase of capped calls	(92,920)	(37,086)	0
Proceeds from tenant improvement allowance on build-to-suit lease	0	1,728	0
Proceeds from initial public offering, net of underwriting discounts and commissions	0	0	205,494
Proceeds from exercise of redeemable convertible preferred stock warrants	0	0	1
Payment of initial public offering costs	0	0	(3,728)
Net cash provided by financing activities	589,238	288,236	209,892
Effect of exchange rate changes on cash, cash equivalents and restricted cash	306	(48)	291
Net increase (decrease) in cash, cash equivalents and restricted cash	558,359	85,920	(6,985)
Cash, cash equivalents and restricted cash, beginning of year	148,347	62,427	69,412
Cash, cash equivalents and restricted cash, end of year	706,706	148,347	62,427
Cash paid during the period for:
Income taxes, net of refunds	2,701	984	1,004
Interest expense, net	2,375	1,044	8
Noncash investing and financing activities
Construction costs related to build-to-suit lease obligations	0	11,683	0
Vesting of early exercised stock options	296	1,204	1,280
Conversion of redeemable convertible preferred stock warrant liability to redeemable convertible preferred stock as a result of warrant exercise	0	0	1,171
Conversion of redeemable convertible preferred stock to common stock	0	0	346,428
Debt issuance and capped call costs included in accounts payable and accrued liabilities	4,200	0	0
Purchases of property and equipment included in accounts payable and accrued liabilities	1,134	66	193
Estimated fair value of office space under a build-to-suit lease	$ 0	$ 0	$ 54,709