Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		26 Months Ended
	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2018
Cash flows from operating activities:
Net income (loss)			$ (16,883)	$ 5,867
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation of property and equipment	$ 600	$ 500	1,263	855
Amortization of intangible assets			2,302	1,147
Amortization/accretion of marketable securities			(106)	101
Stock-based compensation			29,325	27,407
Other non-cash items, net			200	44
Changes in operating assets and liabilities:
Accounts receivable			2,287	245
Inventories			(7,404)	2,419
Prepaid expenses and other current assets			1,318	1,618
Deferred tax assets			(118)	(525)
Other assets			(279)	(5)
Accounts payable			3,566	3,511
Accrued liabilities			(9,054)	(9,293)
Income taxes payable			(412)	1,446
Deferred revenue			318	(1,222)
Other long-term liabilities			654	39
Net cash provided by operating activities			6,977	33,654
Cash flows from investing activities:
Purchase of investments			(39,639)	(28,049)
Sales of investments			15,120	4,500
Maturities of investments			31,750	14,840
Purchase of property and equipment			(1,977)	(1,853)
Net cash provided by (used in) investing activities			5,254	(10,562)
Cash flows from financing activities:
Stock repurchase	(45,000)		(65,614)	(38,720)	$ (140,500)
Proceeds from exercise of stock options and employee stock purchase plan			3,672	3,396
Payment for intangible asset			(1,672)	(901)
Net cash used in financing activities			(63,614)	(36,225)
Net decrease in cash, cash equivalents and restricted cash			(51,383)	(13,133)
Cash, cash equivalents and restricted cash at beginning of period			346,681	322,880
Cash, cash equivalents and restricted cash at end of period	$ 295,298	$ 309,747	295,298	309,747	$ 295,298
Supplemental disclosure of cash flow information:
Cash paid for income taxes			1,009	567
Supplemental disclosure of noncash investing and financing activities:
Unpaid liabilities related to intangible and fixed assets additions			$ 286	$ 9,193