Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Oct. 31, 2016	Oct. 31, 2015
Cash flows from operating activities:
Net income	$ 39,460	$ 71,412
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property and equipment	1,206	1,164
Amortization/accretion of marketable securities	172	415
Loss on disposal of long-lived assets	28	12
Stock-based compensation	35,474	19,548
Other non-cash items, net	29	127
Changes in operating assets and liabilities, net of impact of acquisition:
Accounts receivable	(1,986)	(5,612)
Inventories	(5,173)	(994)
Prepaid expenses and other current assets	(581)	13
Deferred tax assets	604	(19)
Other assets	(45)	(18)
Accounts payable	14,189	1,566
Accrued liabilities	825	(12)
Income taxes payable	572	1,012
Deferred tax liabilities	(58)	(7)
Deferred revenue	(3,192)	1,806
Other long-term liabilities	(476)	2,832
Net cash provided by operating activities	81,048	93,245
Cash flows from investing activities:
Acquisition, net of cash acquired	0	(29,905)
Purchase of investments	(72,950)	(45,957)
Sales of investments	28,368	17,732
Maturities of investments	25,560	25,118
Purchase of property and equipment	(2,070)	(1,289)
Net cash used in investing activities	(21,092)	(34,301)
Cash flows from financing activities:
Stock repurchase	(20,183)	0
Proceeds from exercise of stock options and employee stock purchase plan	5,626	7,230
Net cash provided by (used in) financing activities	(14,557)	7,230
Net increase in cash and cash equivalents	45,399	66,174
Cash and cash equivalents at beginning of period	268,056	170,291
Cash and cash equivalents at end of period	313,455	236,465
Supplemental disclosure of cash flow information:
Cash paid for income taxes	914	831
Supplemental disclosure of noncash investing activities:
Increase in accrued liabilities related to non-monetary assets purchases	$ 34	$ 109