Information with Respect to A Ordinary Shares that were Surrendered or Repurchased (Detail) - Ordinary Shares A - USD ($)		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Equity, Class of Treasury Stock [Line Items]
Total Number of Shares Purchased		0	0	27,028	45,233
Average Price Paid Per Share				$ 35.07	$ 40.07
Total Number of Shares Purchased as Part of Publicly Announced Plan or Program				0	0
Approximate Dollar Value of Shares that May Yet Be Purchased Under the Plans or Programs		$ 0	$ 0	$ 0	$ 0
January 1-31, 2019
Equity, Class of Treasury Stock [Line Items]
Total Number of Shares Purchased	[1],[2]			7,945
Average Price Paid Per Share	[1]			$ 36.23
Total Number of Shares Purchased as Part of Publicly Announced Plan or Program	[1]			0
Approximate Dollar Value of Shares that May Yet Be Purchased Under the Plans or Programs	[1]	0		$ 0
February 1-28, 2019
Equity, Class of Treasury Stock [Line Items]
Total Number of Shares Purchased	[1],[2]			19,083
Average Price Paid Per Share	[1]			$ 34.59
Total Number of Shares Purchased as Part of Publicly Announced Plan or Program	[1]			0
Approximate Dollar Value of Shares that May Yet Be Purchased Under the Plans or Programs	[1]	$ 0		$ 0
January 1-31, 2018
Equity, Class of Treasury Stock [Line Items]
Total Number of Shares Purchased	[1],[2]				26,639
Average Price Paid Per Share	[1]				$ 42.02
Total Number of Shares Purchased as Part of Publicly Announced Plan or Program	[1]				0
Approximate Dollar Value of Shares that May Yet Be Purchased Under the Plans or Programs	[1]		0		$ 0
March 1-31, 2018
Equity, Class of Treasury Stock [Line Items]
Total Number of Shares Purchased	[1],[2]				18,594
Average Price Paid Per Share	[1]				$ 37.27
Total Number of Shares Purchased as Part of Publicly Announced Plan or Program	[1]				0
Approximate Dollar Value of Shares that May Yet Be Purchased Under the Plans or Programs	[1]		$ 0		$ 0

[1] Based on settlement date.

[2] Surrendered by employees as payment of taxes withheld on the vesting of restricted stock.