Consolidated Statements of Cash Flows $ in Thousands	12 Months Ended
	Jan. 31, 2020 USD ($)	Jan. 31, 2019 USD ($)	Jan. 31, 2018 USD ($)
Operating activities:
Net loss	$ (121,544)	$ (74,837)	$ (66,565)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Depreciation and amortization	8,069	6,813	5,123
Provision for bad debts	1,246	492	478
Stock-based compensation expense	67,770	44,233	22,360
Change in fair value of convertible preferred stock warrant liability	0	0	491
Amortization of operating lease right-of-use assets	11,124	0	0
Other, net	120	(83)	166
Changes in operating assets and liabilities:
Accounts receivable	(26,981)	(11,601)	(17,036)
Prepaid expenses and other current assets	268	(6,745)	(4,043)
Costs to obtain revenue contracts	(18,344)	(16,817)	(4,420)
Other long term assets	(2,629)	2	(358)
Accounts payable, accrued expenses and other current liabilities	8,267	17,626	695
Unearned revenue	42,345	47,004	31,753
Operating lease liabilities	(1,044)	0	0
Other long term liabilities	565	(847)	(1,053)
Net cash (used in) provided by operating activities	(30,768)	5,240	(32,409)
Investing activities:
Purchases of marketable securities	0	(52,916)	(110,644)
Maturities of marketable securities	51,197	86,320	20,154
Sales of marketable securities	0	0	6,041
Capital expenditures	(11,889)	(5,270)	(3,674)
Net cash provided by (used in) investing activities	39,308	28,134	(88,123)
Financing activities:
Proceeds from initial public offering, net of underwriting discounts and commissions	0	0	123,527
Proceeds from common stock offering, net of underwriting discounts and commissions	147,000	0	0
Payments of deferred offering costs	(530)	0	(4,263)
Proceeds from exercise of stock options	14,893	18,880	11,610
Proceeds from exercise of warrants	0	0	79
Repayments on Revolving Line	0	0	(5,000)
Payments of deferred financing costs	(260)	(159)	(99)
Proceeds, net from employee stock purchase plan withholdings	7,270	5,663	3,750
Net cash provided by financing activities	168,373	24,384	129,604
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(492)	(370)	375
Net increase in cash, cash equivalents and restricted cash	176,421	57,388	9,447
Cash, cash equivalents and restricted cash at beginning of period	91,755	34,367	24,920
Cash, cash equivalents and restricted cash at end of period	268,176	91,755	34,367
Supplemental disclosures of non-cash investing and financing activities:
Cash paid on interest	41	7	74
Cash paid on income taxes	531	19	994
Non-cash capital expenditures in accounts payable, accrued expenses and other current liabilities	9,194	143	209
Stock-based compensation for capitalized software in property and equipment, net	1,416	675	408
Conversion of convertible preferred stock to common stock	0	0	120,615
Conversion of convertible preferred stock warrants to common stock warrants	0	0	1,435
Supplemental Cash Flow Information [Abstract]
Cash and cash equivalents	256,076	91,755	34,367
Restricted cash	12,100	0	0
Cash, cash equivalents and restricted cash at end of period	$ 268,176	$ 91,755	$ 34,367