Net Income per Share Attributable to Common Stockholders - Numerators and Denominators of the Basic and Diluted EPS Computations for Common Stock (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2015	Apr. 30, 2015	Jan. 31, 2015	Oct. 31, 2014	Jul. 31, 2014	Apr. 30, 2014	Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2014
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income	$ 17,590	$ 10,482	$ 13,406	$ 12,982	$ 13,326	$ 10,258	$ 9,578	$ 7,221	$ 54,460	$ 40,383	$ 23,615
Basic									132,020	127,713	51,725
Net income per share attributable to common stockholders, basic	$ 0.13	$ 0.08	$ 0.10	$ 0.10	$ 0.10	$ 0.08	$ 0.07	$ 0.06	$ 0.41	$ 0.31	$ 0.20
Reallocation as a result of conversion of Class B to Class A common stock:
Number of shares used for basic EPS computation									132,020	127,713	51,725
Weighted average shares used in computing net income per share attributable to common stockholders, diluted									144,977	144,204	68,024
Net income per share attributable to common stockholders, diluted	$ 0.12	$ 0.07	$ 0.09	$ 0.09	$ 0.09	$ 0.07	$ 0.07	$ 0.05	$ 0.38	$ 0.28	$ 0.15
Class A common stock [Member]
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income									$ 31,453	$ 14,540	$ 1,934
Noncumulative dividends on convertible preferred stock											(33)
Undistributed earnings allocated to participating securities									(27)	(88)	(1,049)
Net income attributable to common stockholders, basic									$ 31,426	$ 14,452	$ 852
Basic									76,246	45,983	4,237
Net income per share attributable to common stockholders, basic									$ 0.41	$ 0.31	$ 0.20
Net income attributable to common stockholders, basic									$ 31,426	$ 14,452	$ 852
Reallocation as a result of conversion of Class B to Class A common stock:
Net income attributable to common stockholders, basic									22,987	25,686	9,553
Net income attributable to common stockholders, diluted									$ 54,413	$ 40,138	$ 10,405
Number of shares used for basic EPS computation									76,246	45,983	4,237
Conversion of Class B to Class A common stock									55,774	81,730	47,488
Effect of potentially dilutive common shares									12,957	16,491	16,299
Weighted average shares used in computing net income per share attributable to common stockholders, diluted									144,977	144,204	68,024
Net income per share attributable to common stockholders, diluted									$ 0.38	$ 0.28	$ 0.15
Class B common stock [Member]
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income									$ 23,007	$ 25,843	$ 21,681
Noncumulative dividends on convertible preferred stock											(371)
Undistributed earnings allocated to participating securities									(20)	(157)	(11,757)
Net income attributable to common stockholders, basic									$ 22,987	$ 25,686	$ 9,553
Basic									55,774	81,730	47,488
Net income per share attributable to common stockholders, basic									$ 0.41	$ 0.31	$ 0.20
Net income attributable to common stockholders, basic									$ 22,987	$ 25,686	$ 9,553
Reallocation as a result of conversion of Class B to Class A common stock:
Reallocation of net income to Class B common stock									2,808	1,653	204
Net income attributable to common stockholders, diluted									$ 25,795	$ 27,339	$ 9,757
Number of shares used for basic EPS computation									55,774	81,730	47,488
Effect of potentially dilutive common shares									12,957	16,491	16,299
Weighted average shares used in computing net income per share attributable to common stockholders, diluted									68,731	98,221	63,787
Net income per share attributable to common stockholders, diluted									$ 0.38	$ 0.28	$ 0.15