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 income		$ 141,966	$ 68,804	$ 54,460
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		14,277	13,825	8,464
Amortization of premiums on short-term investments		1,389	1,852	2,804
Stock-based compensation		54,049	40,798	24,258
Deferred income taxes		3,282	(5,073)	(6,264)
Loss on foreign currency from market-to-market derivative		265
Bad debt expense		(242)	130	201
Changes in operating assets and liabilities:
Accounts receivable		(50,673)	(38,148)	(46,653)
Income taxes		(2,520)	911	(2,994)
Prepaid expenses and other current and long-term assets		(2,492)	831	180
Accounts payable		1,396	1,113	(494)
Accrued expenses and other current liabilities		7,149	336	5,042
Deferred revenue		61,773	56,208	39,357
Other long-term liabilities		3,818	2,424	1,793
Net cash provided by operating activities	[1]	233,437	144,011	80,154
Cash flows from investing activities
Purchases of short-term investments		(437,858)	(314,847)	(313,357)
Maturities and sales of short-term investments		294,705	225,600	364,968
Purchases of property and equipment		(9,633)	(6,923)	(21,153)
Acquisitions, net of cash acquired				(126,183)
Purchases of intangible assets				(568)
Capitalized internal-use software development costs		(1,734)	(584)	(431)
Changes in restricted cash and deposits		(202)	102	41
Net cash used in investing activities		(154,722)	(96,652)	(96,683)
Cash flows from financing activities
Proceeds from early exercise of common stock options				10
Proceeds from exercise of common stock options		20,773	12,362	5,875
Restricted stock units acquired to settle employee tax withholding liability			(14)	(6)
Excess tax benefits from employee stock plans			25,628	13,527
Net cash provided by financing activities	[1]	20,773	37,976	19,406
Effect of exchange rate changes on cash and cash equivalents		3,089	92	49
Net change in cash and cash equivalents		102,577	85,427	2,926
Cash and cash equivalents at beginning of period		217,606	132,179	129,253
Cash and cash equivalents at end of period		320,183	217,606	132,179
Supplemental disclosures of other cash flow information:
Cash paid for income taxes, net of refunds		12,461	14,154	19,968
Non-cash investing and financing activities:
Changes in accounts payable and accrued expenses related to property and equipment purchases		(1,388)	460	334
Vesting of early exercised stock options		$ 1	$ 26	70
Zinc Ahead Inc [Member]
Non-cash investing and financing activities:
Working capital adjustment, not yet paid				$ 339

[1] During the fiscal year ended January 31, 2018, we adopted Accounting Standards Update (ASU) 2016-09, “Compensation-Stock Compensation: Improvements to Employee Share-Based Payment.” Refer to note 1—New Accounting Pronouncements Adopted in Fiscal 2018 for further details. This adoption resulted in a $8.6 million and $45.8 million increase in net cash provided by operating activities and a corresponding decrease in net cash provided by financing activities for the three months and fiscal year ended January 31, 2018, respectively.