Net Income per Share - 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, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Weighted average shares used in computing net income per share, basic									147,796	144,244	140,311
Net income per share, basic	$ 0.44	$ 0.56	$ 0.54	$ 0.50	$ 0.49	$ 0.44	$ 0.35	$ 0.31	$ 2.04	$ 1.59	$ 1.08
Reallocation as a result of conversion of Class B to Class A common stock:
Weighted average shares used in computing net income per share, diluted									158,296	156,117	153,681
Net income per share, diluted	$ 0.42	$ 0.52	$ 0.50	$ 0.47	$ 0.45	$ 0.41	$ 0.32	$ 0.29	$ 1.90	$ 1.47	$ 0.98
Class A common stock
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income, basic									$ 266,104
Weighted average shares used in computing net income per share, basic									130,610
Net income per share, basic									$ 2.04
Net income, basic									$ 266,104
Reallocation as a result of conversion of Class B to Class A common stock:
Net income, basic									35,014
Reallocation of net income to Class B common stock									0
Net income, diluted									$ 301,118
Conversion of Class B to Class A common stock									17,186
Effect of potentially dilutive common shares									10,500
Weighted average shares used in computing net income per share, diluted									158,296
Net income per share, diluted									$ 1.90
Class A common stock | As adjusted
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income, basic										$ 194,607	$ 121,203
Weighted average shares used in computing net income per share, basic										122,137	112,491
Net income per share, basic										$ 1.59	$ 1.08
Net income, basic										$ 194,607	$ 121,203
Reallocation as a result of conversion of Class B to Class A common stock:
Net income, basic										35,225	29,974
Reallocation of net income to Class B common stock										0	0
Net income, diluted										$ 229,832	$ 151,177
Conversion of Class B to Class A common stock										22,107	27,820
Effect of potentially dilutive common shares										11,873	13,370
Weighted average shares used in computing net income per share, diluted										156,117	153,681
Net income per share, diluted										$ 1.47	$ 0.98
Class B common stock
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income, basic									$ 35,014
Weighted average shares used in computing net income per share, basic									17,186
Net income per share, basic									$ 2.04
Net income, basic									$ 35,014
Reallocation as a result of conversion of Class B to Class A common stock:
Net income, basic									0
Reallocation of net income to Class B common stock									17,652
Net income, diluted									$ 52,666
Conversion of Class B to Class A common stock									0
Effect of potentially dilutive common shares									10,500
Weighted average shares used in computing net income per share, diluted									27,686
Net income per share, diluted									$ 1.90
Class B common stock | As adjusted
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income, basic										$ 35,225	$ 29,974
Weighted average shares used in computing net income per share, basic										22,107	27,820
Net income per share, basic										$ 1.59	$ 1.08
Net income, basic										$ 35,225	$ 29,974
Reallocation as a result of conversion of Class B to Class A common stock:
Net income, basic										0	0
Reallocation of net income to Class B common stock										14,800	10,545
Net income, diluted										$ 50,025	$ 40,519
Conversion of Class B to Class A common stock										0	0
Effect of potentially dilutive common shares										11,873	13,370
Weighted average shares used in computing net income per share, diluted										33,980	41,190
Net income per share, diluted										$ 1.47	$ 0.98