Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2014
Cash flows from operating activities:
Net income	$ 76,508	$ 50,571	$ 25,654
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property and equipment	1,606	1,335	1,096
Amortization/accretion of marketable securities	525	675	0
Loss on disposal of long-lived assets	13	21	13
Stock-based compensation	31,094	15,692	8,535
Excess income tax benefits associated with stock-based compensation	0	(3,286)	(903)
Other non-cash items, net	142	26	0
Changes in operating assets and liabilities, net of effects of acquisitions:
Accounts receivable	1,262	(21,343)	1,316
Inventories	3,627	(11,241)	(1,534)
Prepaid expenses and other current assets	(572)	(563)	(375)
Deferred tax assets	1,291	(3,184)	(442)
Other assets	(114)	307	63
Accounts payable	(6,880)	12,715	1,270
Accrued liabilities	4,189	6,837	(2,642)
Income taxes payable	244	3,490	807
Deferred tax liabilities	43	83	9
Deferred revenue	4,939	274	1,380
Other long-term liabilities	5,644	(151)	103
Net cash provided by operating activities	123,561	52,258	34,350
Cash flows from investing activities:
Acquisition, net of cash acquired	(29,905)	0	0
Investment in a private company	0	(290)	0
Purchase of investments	(52,786)	(59,807)	0
Sales of investments	17,732	8,729	0
Maturities of investments	32,248	12,668	0
Net proceeds from disposal of fixed assets	0	0	13
Purchase of property and equipment	(2,085)	(1,361)	(1,701)
Net cash used in investing activities	(34,796)	(40,061)	(1,688)
Cash flows from financing activities:
Proceeds from exercise of stock options, warrants, and employee stock purchase plan, net of repurchase of stock options	9,000	11,414	9,360
Payment for initial public offering cost	0	0	(25)
Excess income tax benefits associated with stock-based compensation	0	3,286	903
Net cash provided by financing activities	9,000	14,700	10,238
Net increase in cash and cash equivalents	97,765	26,897	42,900
Cash and cash equivalents at beginning of period	170,291	143,394	100,494
Cash and cash equivalents at end of period	268,056	170,291	143,394
Supplemental disclosure of cash flow information:
Cash paid for income taxes	1,618	1,069	1,766
Supplemental disclosure of noncash investing activities:
Increase in accrued liabilities related to non-monetary assets purchases	$ 43	$ 75	$ 24