Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Apr. 30, 2015	Apr. 30, 2014
Cash flows from operating activities:
Net income	$ 18,854	$ 5,260
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property and equipment	367	299
Amortization/accretion of marketable securities	150	104
Loss on disposal of long-lived assets	7	1
Stock-based compensation	5,482	2,874
Excess income tax benefits associated with stock-based compensation	(183)	(274)
Other non-cash items, net	75	(3)
Changes in operating assets and liabilities:
Accounts receivable	987	(2,468)
Inventories	(4,110)	418
Prepaid expenses and other current assets	833	530
Deferred tax assets	(132)	(126)
Other assets	(26)	43
Accounts payable	2,954	5,087
Accrued liabilities	(2,487)	(1,639)
Income taxes payable	741	178
Deferred tax liabilities	(20)	0
Deferred revenue	1,301	(14)
Net cash provided by operating activities	24,793	10,270
Cash flows from investing activities:
Purchase of investments	(14,284)	(27,306)
Sales of investments	5,478	7
Maturities of investments	8,350	905
Purchase of property and equipment	(376)	(224)
Net cash used in investing activities	(832)	(26,618)
Cash flows from financing activities:
Proceeds from exercise of stock options and employee stock purchase plan	2,876	2,160
Excess income tax benefits associated with stock-based compensation	183	274
Net cash provided by financing activities	3,059	2,434
Net increase (decrease) in cash and cash equivalents	27,020	(13,914)
Cash and cash equivalents at beginning of period	170,291	143,394
Cash and cash equivalents at end of period	197,311	129,480
Supplemental disclosure of cash flow information:
Cash paid for income taxes	174	134
Supplemental disclosure of noncash investing activities:
Increase in accrued liabilities related to non-monetary assets purchases	$ 20	$ 30