Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Cash flows from operating activities:
Net income	$ 57,810	$ 76,508	$ 50,571
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property and equipment	1,585	1,606	1,335
Amortization/accretion of marketable securities	246	525	675
Loss on disposal of long-lived assets	43	13	21
Stock-based compensation	48,832	31,094	15,692
Excess income tax benefits associated with stock-based compensation	0	0	(3,286)
Other non-cash items, net	40	142	26
Changes in operating assets and liabilities, net of effects of acquisitions:
Accounts receivable	812	1,262	(21,343)
Inventories	(1,978)	3,627	(11,241)
Prepaid expenses and other current assets	(216)	(572)	(563)
Deferred tax assets	853	1,291	(3,184)
Other assets	(107)	(114)	307
Accounts payable	5,780	(6,880)	12,715
Accrued liabilities	2,069	4,189	6,837
Income taxes payable	(219)	244	3,490
Deferred tax liabilities	(89)	43	83
Deferred revenue	(2,652)	4,939	274
Other long-term liabilities	505	5,644	(151)
Net cash provided by operating activities	113,314	123,561	52,258
Cash flows from investing activities:
Acquisition, net of cash acquired	0	(29,905)	0
Investment in a private company	0	0	(290)
Purchase of investments	(115,546)	(52,786)	(59,807)
Sales of investments	31,078	17,732	8,729
Maturities of investments	41,435	32,248	12,668
Purchase of property and equipment	(2,701)	(2,085)	(1,361)
Net cash used in investing activities	(45,734)	(34,796)	(40,061)
Cash flows from financing activities:
Proceeds from exercise of stock options and employee stock purchase plan	7,419	9,000	11,414
Stock repurchase	(20,183)	0	0
Excess income tax benefits associated with stock-based compensation	0	0	3,286
Net cash provided by (used in) financing activities	(12,764)	9,000	14,700
Net increase in cash and cash equivalents	54,816	97,765	26,897
Cash and cash equivalents at beginning of period	268,056	170,291	143,394
Cash and cash equivalents at end of period	322,872	268,056	170,291
Supplemental disclosure of cash flow information:
Cash paid for income taxes	2,070	1,618	1,069
Supplemental disclosure of noncash investing activities:
Increase in accrued liabilities related to non-monetary assets purchases	$ 481	$ 43	$ 75