Capital Stock - Additional Information (Detail) - USD ($)			12 Months Ended			32 Months Ended
	Jun. 04, 2018	Jun. 30, 2016	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2019
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
Ordinary shares, shares authorized			200,000,000	200,000,000		200,000,000
Stock repurchase program, expiration date			Jun. 04, 2019
Stock repurchased during period, shares			2,485,992
Stock repurchased during period, cash			$ 99,904,000	$ 54,788,000	$ 20,183,000
Amount available under stock repurchase program			31,900,000			$ 31,900,000
Stock Repurchase Program $225.0 Million Authorization [Member]
Class Of Stock [Line Items]
Stock repurchase program, authorization date		Jun. 30, 2016
Stock repurchased during period, shares						3,985,876
Stock repurchased during period, cash						$ 174,800,000
Stock Repurchase Program $100.0 Million Authorization [Member]
Class Of Stock [Line Items]
Stock repurchase program, authorization date	Jun. 04, 2018
Stock repurchase program, period	12 months
Stock repurchase program, commencing date	Jun. 05, 2018
Maximum [Member] | Stock Repurchase Program $225.0 Million Authorization [Member]
Class Of Stock [Line Items]
Amount authorized under stock repurchase program			$ 225,000,000			$ 225,000,000
Maximum [Member] | Stock Repurchase Program $100.0 Million Authorization [Member]
Class Of Stock [Line Items]
Amount authorized under stock repurchase program	$ 100,000,000