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			9 Months Ended
		Oct. 31, 2018	Oct. 31, 2017		Oct. 31, 2018	Oct. 31, 2017
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income		$ 64,085	$ 34,925	[1]	$ 158,681	$ 110,523	[1]
Weighted average shares used in computing net income per share attributable to common stockholders, basic		144,737	140,857	[1]	143,765	139,858	[1]
Net income per share attributable to common stockholders, basic		$ 0.44	$ 0.25	[1]	$ 1.10	$ 0.79	[1]
Reallocation as a result of conversion of Class B to Class A common stock:
Weighted average shares used in computing net income per share attributable to common stockholders, diluted		156,025	154,256	[1]	155,706	153,409	[1]
Net income per share attributable to common stockholders, diluted		$ 0.41	$ 0.23	[1]	$ 1.02	$ 0.72	[1]
Class A common stock [Member]
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income		$ 54,592			$ 133,568
Net income attributable to common stockholders, basic		$ 54,592			$ 133,568
Weighted average shares used in computing net income per share attributable to common stockholders, basic		123,297			121,013
Net income per share attributable to common stockholders, basic		$ 0.44			$ 1.10
Net income attributable to common stockholders, basic		$ 54,592			$ 133,568
Reallocation as a result of conversion of Class B to Class A common stock:
Net income attributable to common stockholders, basic		9,493			25,113
Net income attributable to common stockholders, diluted		$ 64,085			$ 158,681
Conversion of Class B to Class A common stock		21,440			22,752
Effect of potentially dilutive common shares		11,288			11,941
Weighted average shares used in computing net income per share attributable to common stockholders, diluted		156,025			155,706
Net income per share attributable to common stockholders, diluted		$ 0.41			$ 1.02
Class A common stock [Member] | As adjusted [Member]
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income	[1]		$ 28,463			$ 87,791
Net income attributable to common stockholders, basic	[1]		$ 28,463			$ 87,791
Weighted average shares used in computing net income per share attributable to common stockholders, basic	[1]		114,794			111,093
Net income per share attributable to common stockholders, basic	[1]		$ 0.25			$ 0.79
Net income attributable to common stockholders, basic	[1]		$ 28,463			$ 87,791
Reallocation as a result of conversion of Class B to Class A common stock:
Net income attributable to common stockholders, basic	[1]		6,462			22,732
Net income attributable to common stockholders, diluted	[1]		$ 34,925			$ 110,523
Conversion of Class B to Class A common stock	[1]		26,063			28,765
Effect of potentially dilutive common shares	[1]		13,399			13,551
Weighted average shares used in computing net income per share attributable to common stockholders, diluted	[1]		154,256			153,409
Net income per share attributable to common stockholders, diluted	[1]		$ 0.23			$ 0.72
Class B common stock [Member]
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income		$ 9,493			$ 25,113
Net income attributable to common stockholders, basic		$ 9,493			$ 25,113
Weighted average shares used in computing net income per share attributable to common stockholders, basic		21,440			22,752
Net income per share attributable to common stockholders, basic		$ 0.44			$ 1.10
Net income attributable to common stockholders, basic		$ 9,493			$ 25,113
Reallocation as a result of conversion of Class B to Class A common stock:
Reallocation of net income to Class B common stock		3,950			10,243
Net income attributable to common stockholders, diluted		$ 13,443			$ 35,356
Effect of potentially dilutive common shares		11,288			11,941
Weighted average shares used in computing net income per share attributable to common stockholders, diluted		32,728			34,693
Net income per share attributable to common stockholders, diluted		$ 0.41			$ 1.02
Class B common stock [Member] | As adjusted [Member]
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income	[1]		$ 6,462			$ 22,732
Net income attributable to common stockholders, basic	[1]		$ 6,462			$ 22,732
Weighted average shares used in computing net income per share attributable to common stockholders, basic	[1]		26,063			28,765
Net income per share attributable to common stockholders, basic	[1]		$ 0.25			$ 0.79
Net income attributable to common stockholders, basic	[1]		$ 6,462			$ 22,732
Reallocation as a result of conversion of Class B to Class A common stock:
Reallocation of net income to Class B common stock	[1]		2,473			7,754
Net income attributable to common stockholders, diluted	[1]		$ 8,935			$ 30,486
Effect of potentially dilutive common shares	[1]		13,399			13,551
Weighted average shares used in computing net income per share attributable to common stockholders, diluted	[1]		39,462			42,316
Net income per share attributable to common stockholders, diluted	[1]		$ 0.23			$ 0.72

[1] See note 1 of the notes to the condensed consolidated financial statements for a summary of adjustments.