Consolidated Statements Stockholders' Equity (USD $) In Thousands, except Share data	Total	Series A and B Convertible Preferred Stock [Member]	Class A & B Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]
Beginning balance, value at Jan. 31, 2012	$ 14,103	$ 6,933		$ 1,026	$ 6,144
Beginning balance, shares at Jan. 31, 2012		85,000,000	22,620,207
Issuance of common stock upon exercise of stock options, value	136			136
Issuance of common stock upon exercise of stock options, shares			1,481,017
Issuance of common stock upon early exercise of stock options			742,627
Vesting of early exercised stock options	224			224
Stock-based compensation expense	715			715
Other comprehensive income	5					5
Net income	18,783				18,783
Ending balance, value at Jan. 31, 2013	33,966	6,933		2,101	24,927	5
Ending balance, shares at Jan. 31, 2013		85,000,000	24,843,851
Issuance of common stock upon exercise of stock options, value	514			514
Issuance of common stock upon exercise of stock options, shares			2,913,194
Issuance of common stock upon early exercise of stock options			357,750
Vesting of early exercised stock options	572			572
Stock-based compensation expense	7,041			7,041
Conversion of preferred stock to common stock, value		(6,933)	1	6,932
Conversion of preferred stock to common stock, shares		(85,000,000)	85,000,000
Initial public/Follow-on offering, net of issuance costs, value	214,200			214,200
Initial public/Follow-on offering, net of issuance costs, shares			11,676,750
Excess tax benefits from employee stock plans	174			174
Other comprehensive income	14					14
Net income	23,615				23,615
Ending balance, value at Jan. 31, 2014	280,096		1	231,534	48,542	19
Ending balance, shares at Jan. 31, 2014			124,791,545
Issuance of common stock upon exercise of stock options, value	5,813			5,813
Issuance of common stock upon exercise of stock options, shares	4,437,349		4,437,349
Vesting of early exercised stock options	377			377
Repurchase of unvested early exercised stock options			(16,667)
Issuance of common stock upon vesting of restricted stock units, value	(15)			(15)
Issuance of common stock upon vesting of restricted stock units, shares			115,339
Stock-based compensation expense	14,385			14,385
Issuance of common shares under Employee Stock Purchase Plan, value	5,951			5,951
Issuance of common shares under Employee Stock Purchase Plan, shares			350,059
Initial public/Follow-on offering, net of issuance costs, value	34,495			34,495
Initial public/Follow-on offering, net of issuance costs, shares			1,390,000
Excess tax benefits from employee stock plans	25,341			25,341
Other comprehensive income	7					7
Net income	40,383				40,383
Ending balance, value at Jan. 31, 2015	$ 406,833		$ 1	$ 317,881	$ 88,925	$ 26
Ending balance, shares at Jan. 31, 2015			131,067,625