Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Oct. 31, 2014	Oct. 31, 2013	Oct. 31, 2014	Oct. 31, 2013
Cash flows from operating activities
Net income	$ 10,258	$ 6,525	$ 27,057	$ 17,368
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	1,022	774	2,943	1,552
Amortization of premiums on short-term investments	611	98	1,344	276
Stock-based compensation	3,585	2,086	10,241	4,036
Deferred income taxes	(76)	(86)	(76)	(259)
Bad debt expense	(28)	(303)	41	(21)
Changes in operating assets and liabilities:
Accounts receivable	16,684	(9,417)	13,151	(9,852)
Income taxes	769	(1,750)	(2,189)	(5,733)
Other current and long-term assets	(2,294)	(1,224)	(3,644)	(2,117)
Accounts payable	354	1,157	56	(946)
Accrued expenses and other current liabilities	4,017	1,720	2,791	5,859
Deferred revenue	(635)	5,254	17,288	14,607
Long-term liabilities	(11)	433	(9)	758
Net cash provided by operating activities	34,256	5,267	68,994	25,528
Cash flows from investing activities
Purchases of short-term investments	(103,836)	(4,315)	(333,728)	(7,086)
Maturities and sales of investments	52,677	2,250	97,307	4,850
Purchases of property and equipment	(790)	(460)	(26,072)	(1,561)
Acquisitions, net of cash acquired				(12,149)
Payments for capitalized internal-use software	(81)	(720)	(301)	(1,013)
Proceeds from note receivable–related party				253
Payments for restricted cash and deposits	8	(5)	9	(2)
Net cash used in investing activities	(52,022)	(3,250)	(262,785)	(16,708)
Cash flows from financing activities
Proceeds from early exercise of common stock options		158		225
Proceeds from exercise of common stock options	2,102	95	4,314	472
Proceeds from Employee Stock Purchase Plan			5,951
Net proceeds from offerings		216,263	34,495	215,734
Excess tax benefits from employee stock plans	7,698		18,731
Net cash provided by financing activities	9,800	216,516	63,491	216,431
Effect of exchange rate changes on cash and cash equivalents	(15)		(72)
Net change in cash and cash equivalents	(7,981)	218,533	(130,372)	225,251
Cash and cash equivalents at beginning of period	140,116	38,608	262,507	31,890
Cash and cash equivalents at end of period	132,135	257,141	132,135	257,141
Supplemental disclosures of other cash flow information:
Cash paid for income taxes	477	4,998	5,101	14,984
Non-cash investing and financing activities:
Changes in accounts payable and accrued liabilities related to property and equipment purchases	191	(46)	170	(20)
Vesting of early exercised stock options	87	212	318	460
Offering costs not yet paid		$ 805		$ 1,473