Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Oct. 31, 2015	Oct. 31, 2014
Cash flows from operating activities:
Net income	$ 71,412	$ 32,897
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property and equipment	1,164	963
Amortization/accretion of marketable securities	415	475
Loss on disposal of long-lived assets	12	16
Stock-based compensation	19,548	10,107
Excess income tax benefits associated with stock-based compensation	0	(451)
Other non-cash items, net	127	(20)
Changes in operating assets and liabilities:
Accounts receivable	(5,612)	(22,128)
Inventories	(994)	(4,387)
Prepaid expenses and other current assets	13	740
Deferred tax assets	(19)	(789)
Other assets	(18)	226
Accounts payable	1,566	12,509
Accrued liabilities	2,820	3,494
Income taxes payable	1,012	1,801
Deferred tax liabilities	(7)	0
Deferred revenue	1,806	347
Net cash provided by operating activities	93,245	35,800
Cash flows from investing activities:
Acquisition, net of cash acquired	(29,905)	0
Investment in a private company	0	(290)
Purchase of investments	(45,957)	(47,417)
Sales of investments	17,732	657
Maturities of investments	25,118	6,340
Purchase of property and equipment	(1,289)	(1,117)
Net cash used in investing activities	(34,301)	(41,827)
Cash flows from financing activities:
Proceeds from exercise of stock options and employee stock purchase plan	7,230	8,759
Excess income tax benefits associated with stock-based compensation	0	451
Net cash provided by financing activities	7,230	9,210
Net increase (decrease) in cash and cash equivalents	66,174	3,183
Cash and cash equivalents at beginning of period	170,291	143,394
Cash and cash equivalents at end of period	236,465	146,577
Supplemental disclosure of cash flow information:
Cash paid for income taxes	831	551
Supplemental disclosure of noncash investing activities:
Increase in accrued liabilities related to non-monetary assets purchases	$ 109	$ 49