Net Income per Share Attributable to Common Stockholders - Numerators and Denominators of the Basic and Diluted EPS Computations for Common Stock (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Jan. 31, 2015	Oct. 31, 2014	Jul. 31, 2014	Apr. 30, 2014	Jan. 31, 2014	Oct. 31, 2013	Jul. 31, 2013	Apr. 30, 2013	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income	$ 13,326	$ 10,258	$ 9,578	$ 7,221	$ 6,247	$ 6,525	$ 5,998	$ 4,845	$ 40,383	$ 23,615	$ 18,783
Basic	130,345	129,212	127,314	123,902	122,578	35,802	24,418	21,610	127,713	51,725	20,887
Net income per share attributable to common stockholders, basic	$ 0.10	$ 0.08	$ 0.07	$ 0.06	$ 0.05	$ 0.07	$ 0.05	$ 0.04	$ 0.31	$ 0.20	$ 0.17
Reallocation as a result of conversion of Class B to Class A common stock:
Number of shares used for basic EPS computation	130,345	129,212	127,314	123,902	122,578	35,802	24,418	21,610	127,713	51,725	20,887
Conversion of Class B to Class A common stock									81,730	47,488
Weighted average shares used in computing net income per share attributable to common stockholders, diluted	144,737	144,289	143,353	142,849	143,221	131,963	37,038	32,988	144,204	68,024	30,599
Net income per share attributable to common stockholders, diluted	$ 0.09	$ 0.07	$ 0.07	$ 0.05	$ 0.04	$ 0.05	$ 0.03	$ 0.03	$ 0.28	$ 0.15	$ 0.11
Class A common stock [Member]
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income									14,540	1,934
Noncumulative dividends on convertible preferred stock										(33)
Undistributed earnings allocated to participating securities									(88)	(1,049)
Net income attributable to common stockholders, basic									14,452	852
Basic									45,983	4,237
Net income per share attributable to common stockholders, basic									$ 0.31	$ 0.20
Net income attributable to common stockholders, basic									14,452	852
Reallocation as a result of conversion of Class B to Class A common stock:
Net income attributable to common stockholders, basic									25,686	9,553
Net income attributable to common stockholders, diluted									40,138	10,405
Number of shares used for basic EPS computation									45,983	4,237
Effect of potentially dilutive common shares									16,491	16,299
Weighted average shares used in computing net income per share attributable to common stockholders, diluted									144,204	68,024
Net income per share attributable to common stockholders, diluted									$ 0.28	$ 0.15
Class B common stock [Member]
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income									25,843	21,681	18,783
Noncumulative dividends on convertible preferred stock										(371)	(560)
Undistributed earnings allocated to participating securities									(157)	(11,757)	(14,743)
Net income attributable to common stockholders, basic									25,686	9,553	3,480
Basic									81,730	47,488	20,887
Net income per share attributable to common stockholders, basic									$ 0.31	$ 0.20	$ 0.17
Net income attributable to common stockholders, basic									25,686	9,553	3,480
Reallocation as a result of conversion of Class B to Class A common stock:
Reallocation of net income to Class B common stock									1,653	204
Net income attributable to common stockholders, diluted									$ 27,339	$ 9,757	$ 3,480
Number of shares used for basic EPS computation									81,730	47,488	20,887
Effect of potentially dilutive common shares									16,491	16,299	9,712
Weighted average shares used in computing net income per share attributable to common stockholders, diluted									98,221	63,787	30,599
Net income per share attributable to common stockholders, diluted									$ 0.28	$ 0.15	$ 0.11