Capital Stock - Additional Information (Detail) - USD ($)			12 Months Ended			44 Months Ended
	May 29, 2019	Jun. 30, 2016	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2020
Class Of Stock [Line Items]
Preference shares, shares authorized			20,000,000	20,000,000		20,000,000
Preference shares, par value			$ 0.00045	$ 0.00045		$ 0.00045
Preference shares, shares issued			0	0		0
Preference shares, shares outstanding			0	0		0
Amount authorized under stock repurchase program			$ 275,000,000.0			$ 275,000,000.0
Stock repurchase program, inception period		2016-06
Stock repurchase program, expiration date			Jun. 30, 2020
Stock repurchased since the inception of repurchase programs, shares			0			3,985,876
Stock repurchased since the inception of repurchase programs, cash			$ 0	$ 99,904,000	$ 54,788,000	$ 174,800,000
Amount available under stock repurchase program			$ 50,000,000.0			$ 50,000,000.0
Stock Repurchase Program $50.0 Million Authorization [Member]
Class Of Stock [Line Items]
Stock repurchase program, authorization date	May 29, 2019
Stock repurchase program, expiration date	Jun. 30, 2020
Stock Repurchase Program $50.0 Million Authorization [Member] | Maximum [Member]
Class Of Stock [Line Items]
Amount authorized under stock repurchase program	$ 50,000,000.0