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 (loss)	$ (30,447)	$ 18,852	$ 57,810
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation of property and equipment	2,571	1,789	1,535
Amortization of intangible assets	4,650	2,981	50
Amortization/accretion of marketable debt securities	(670)	172	246
Stock-based compensation	60,812	56,861	48,832
Deferred income taxes	(6,945)	2,092	764
Other non-cash items, net	350	165	85
Changes in operating assets and liabilities:
Accounts receivable	5,082	7,302	812
Inventories	5,131	(3,238)	(1,978)
Prepaid expenses and other current assets	(2,202)	379	(216)
Other non-current assets	(155)	(33)	(107)
Accounts payable	(7,014)	(140)	5,780
Accrued liabilities	(8,302)	1,430	2,069
Income taxes payable	57	368	(219)
Deferred revenue	265	(7,026)	(2,652)
Other long-term liabilities	1,289	3,450	505
Net cash provided by operating activities	24,472	85,404	113,316
Cash flows from investing activities:
Purchase of investments	(207,841)	(74,863)	(115,546)
Sales of investments	66,211	10,900	31,078
Maturities of investments	65,428	58,050	41,435
Purchase of property and equipment	(2,940)	(3,687)	(2,701)
Net cash used in investing activities	(79,142)	(9,600)	(45,734)
Cash flows from financing activities:
Proceeds from exercise of stock options and employee stock purchase plan	6,686	7,091	7,419
Stock repurchase	(99,904)	(54,788)	(20,183)
Payment for intangible assets	(4,735)	(4,306)	0
Net cash used in financing activities	(97,953)	(52,003)	(12,764)
Net increase (decrease) in cash, cash equivalents and restricted cash	(152,623)	23,801	54,818
Cash, cash equivalents and restricted cash at beginning of period	346,681	322,880	268,062
Cash, cash equivalents and restricted cash at end of period	194,058	346,681	322,880
Supplemental disclosure of cash flow information:
Cash paid for income taxes	1,409	845	2,070
Supplemental disclosure of noncash investing activities:
Unpaid liabilities related to intangible and fixed assets purchases	$ 933	$ 9,008	$ 481