Capital Stock - Additional Information (Detail) - USD ($)					6 Months Ended	50 Months Ended
	May 29, 2020	Mar. 16, 2020	Feb. 01, 2020	Jun. 30, 2016	Jul. 31, 2020	Jul. 31, 2020	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
Ordinary shares, shares authorized					200,000,000	200,000,000	200,000,000
Amount authorized under stock repurchase program					$ 275,000,000.0	$ 275,000,000.0
Stock repurchased, shares						4,011,595
Stock repurchased during period, cash					1,000,000	$ 175,800,000
Stock repurchase program, inception period				2016-06
2012 Equity Incentive Plan [Member]
Class Of Stock [Line Items]
Additional ordinary shares reserved for issuance			1,521,252
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			422,570
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 $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 repurchased, shares		25,719
Stock repurchased during period, cash		$ 1,000,000.0
Stock repurchase program, extended expiration period	12 months
Stock repurchase program, extended expiration date	Jun. 30, 2021
Amount available under stock repurchase program					$ 49,000,000.0	$ 49,000,000.0
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