Consolidated Statements of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Jan. 31, 2019	Jan. 31, 2018		Jan. 31, 2017
Cash flows from operating activities
Net income		$ 229,832	$ 151,177	[1]	$ 77,572	[1]
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		14,071	14,277	[1]	13,825	[1]
Amortization of premiums (accretion of discount) on short-term investments		(2,431)	1,389	[1]	1,852	[1]
Stock-based compensation		76,425	54,049	[1]	40,798	[1]
Amortization of deferred costs		18,378	16,647	[1]	14,187	[1]
Deferred income taxes		(8,091)	1,209	[1]	(1,120)	[1]
(Gain) Loss on foreign currency from market-to-market derivative		(177)	265	[1]
Bad debt expense (recovery)		198	(242)	[1]	130	[1]
Changes in operating assets and liabilities:
Accounts receivable		(78,995)	(47,799)	[1]	(36,647)	[1]
Unbilled accounts receivable		(4,774)	(4,329)	[1]	(3,026)	[1]
Deferred costs		(18,941)	(18,795)	[1]	(20,408)	[1]
Income taxes		637	(2,520)	[1]	911	[1]
Prepaid expenses and other current and long-term assets		(10,562)	(2,493)	[1]	831	[1]
Accounts payable		1,822	1,396	[1]	1,113	[1]
Accrued expenses and other current liabilities		963	7,149	[1]	336	[1]
Deferred revenue		89,416	58,240	[1]	51,234	[1]
Other long-term liabilities		3,056	3,818	[1]	2,423	[1]
Net cash provided by operating activities		310,827	233,438	[1]	144,011	[1]
Cash flows from investing activities
Purchases of short-term investments		(726,379)	(437,858)	[1]	(314,847)	[1]
Maturities and sales of short-term investments		632,329	294,705	[1]	225,600	[1]
Purchases of property and equipment		(8,440)	(9,633)	[1]	(6,923)	[1]
Capitalized internal-use software development costs		(1,379)	(1,734)	[1]	(584)	[1]
Net cash used in investing activities		(103,869)	(154,520)	[1]	(96,754)	[1]
Cash flows from financing activities
Proceeds from exercise of common stock options		25,910	20,773	[1]	12,362	[1]
Restricted stock units acquired to settle employee tax withholding liability	[1]				(14)
Excess tax benefits from employee stock plans	[1]				25,628
Net cash provided by financing activities		25,910	20,773	[1]	37,976	[1]
Effect of exchange rate changes on cash, cash equivalents, and restricted cash		(2,077)	3,089	[1]	91	[1]
Net change in cash, cash equivalents, and restricted cash		230,791	102,780	[1]	85,324	[1]
Cash, cash equivalents, and restricted cash at beginning of period	[1]	321,387	218,607		133,283
Cash, cash equivalents, and restricted cash at end of period		552,178	321,387	[1]	218,607	[1]
Cash, cash equivalents, and restricted cash at end of period:
Cash and cash equivalents		550,971	320,183	[1]	217,606	[1]
Restricted cash included in other long-term assets		1,207	1,204	[1]	1,001	[1]
Cash, cash equivalents, and restricted cash at end of period		552,178	321,387	[1]	218,607	[1]
Supplemental disclosures of other cash flow information:
Cash paid for income taxes, net of refunds		19,541	12,461	[1]	14,154	[1]
Excess tax benefits from employee stock plans		45,830	45,864	[1]	25,628	[1]
Non-cash investing and financing activities:
Changes in accounts payable and accrued expenses related to property and equipment purchases		$ 644	(1,388)	[1]	460	[1]
Vesting of early exercised stock options	[1]		$ 1		$ 26

[1] See note 1 of the notes to the consolidated financial statements for a summary of adjustments.