Capital Stock - Additional Information (Detail) - USD ($)			3 Months Ended	6 Months Ended		26 Months Ended
	Jun. 04, 2018	Mar. 30, 2018	Jul. 31, 2018	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2018	Jan. 31, 2018
Class Of Stock [Line Items]
Preference shares, shares authorized			20,000,000	20,000,000		20,000,000	20,000,000
Preference shares, par value			$ 0.00045	$ 0.00045		$ 0.00045	$ 0.00045
Preference shares, shares issued			0	0		0	0
Preference shares, shares outstanding			0	0		0	0
Ordinary shares, shares authorized			200,000,000	200,000,000		200,000,000	200,000,000
Stock repurchase program, expiration date				Jun. 04, 2019
Stock repurchase program, period	12 months
Stock repurchase program, commencing date	Jun. 05, 2018
Stock repurchased during period, shares			1,119,193	1,556,641		3,056,525
Stock repurchased during period, cash			$ 45,000,000	$ 65,614,000	$ 38,720,000	$ 140,500,000
Amount available under stock repurchase program			$ 66,100,000	$ 66,100,000		$ 66,100,000
2012 Equity Incentive Plan [Member]
Class Of Stock [Line Items]
Additional ordinary shares reserved for issuance		1,507,032
2012 Equity Incentive Plan [Member] | Scenario, plan automatically increased by the lessor of [Member]
Class Of Stock [Line Items]
Annual increase in ordinary shares for available for future issuance		3,500,000
Annual shares increase for future issuance by percentage under 2012 equity incentive plan		4.50%
Amended and Restated 2012 Employee Stock Purchase Plan [Member]
Class Of Stock [Line Items]
Additional ordinary shares reserved for issuance		418,620
Amended and Restated 2012 Employee Stock Purchase Plan [Member] | Scenario, plan automatically increased by the lessor of [Member]
Class Of Stock [Line Items]
Annual increase in ordinary shares for available for future issuance		1,500,000
Annual shares increase for future issuance by percentage under 2012 employee stock purchase plan		1.25%
Stock Repurchase Program $100.0 Million Authorization [Member]
Class Of Stock [Line Items]
Stock repurchase program, authorization date	Jun. 04, 2018
Stock repurchase program, expiration date	Jun. 04, 2019
Stock Repurchase Program $100.0 Million Authorization [Member] | Maximum [Member]
Class Of Stock [Line Items]
Amount authorized under stock repurchase program	$ 100,000,000