Share-based Compensation - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jun. 29, 2004
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Options outstanding	1,086,822	1,137,179
Options exercisable	608,320
Income tax benefit related to expense	$ 3,400,000	$ 4,300,000	$ 1,600,000
Closing stock price	$ 54.70
Share-based compensation	$ 12,557,000	15,966,000	7,214,000
2012 LTIP Plan [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Award Contractual term	10 years
Amount of shares reserved for issuance	3,200,000
Options outstanding	881,322
Options exercisable	402,820
2004 LTIP Plan [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Amount of shares reserved for issuance				3,100,000
Stock Purchase Plan [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Amount of shares reserved for issuance	1,850,000
Maximum percentage of compensation eligible employees to be deducted for purchase of common stock	25.00%
Purchase price of shares equivalent to fair market value	85.00%
Shares issued under stock purchase plan	1,504,445
Stock Purchase Plan [Member] | Minimum [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Percentage of compensation eligible employees to be deducted for purchase of common stock	1.00%
Restricted Stock [Member] | 2012 LTIP Plan [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Unvested restricted stock and stock units outstanding	381,204
Performance Stock Units [Member] | 2012 LTIP Plan [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Unvested restricted stock and stock units outstanding	241,864
Staff Share Option Plan [Member] | 2004 LTIP Plan [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Options outstanding	55,500
Unvested restricted stock and stock units outstanding	0
Stock Option [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Service period	4 years
Unamortized compensation expense	$ 2,900,000
Weighted-average period for unamortized compensation cost expected to be recognized	1 year 6 months
Total intrinsic value of options exercised	$ 2,200,000	4,300,000	700,000
Aggregate intrinsic value of options outstanding	18,700,000	3,300,000	8,000,000
Aggregate intrinsic value of options exercisable	12,400,000	2,200,000	4,300,000
Share-based compensation	2,388,000	2,021,000	1,437,000
Time-based Restricted Stock Awards and Stock Units [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Unamortized compensation expense	$ 11,000,000
Weighted-average period for unamortized compensation cost expected to be recognized	2 years 4 months 24 days
Non-vested shares	143,469
Vesting period	4 years
Non-vested shares, vested in period	$ 7,300,000	7,200,000	6,100,000
Aggregate intrinsic value of restricted stock outstanding	17,800,000	$ 13,000,000	$ 14,900,000
Performance-based Restricted Stock Awards [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Unamortized compensation expense	$ 400,000
Weighted-average period for unamortized compensation cost expected to be recognized	1 year
Non-vested shares	0	0	110,660
Non-vested shares, vested in period	$ 4,900,000	$ 0	$ 0
Aggregate intrinsic value of restricted stock outstanding	3,000,000	7,000,000	7,600,000
Share-based compensation	462,000	$ 5,716,000	0
Market-based PSUs [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Unamortized compensation expense	$ 5,900,000
Weighted-average period for unamortized compensation cost expected to be recognized	2 years
Non-vested shares	94,902	96,245
Aggregate intrinsic value of restricted stock outstanding	$ 10,200,000	$ 3,500,000	0
Share-based compensation	$ 2,904,000	$ 948,000	$ 0
Common stock issued based on performance stock units	1
Percentage of performance to be achieved	100.00%
Market-based PSUs [Member] | July 2017 Grant Date [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Performance period	3 years
Market-based PSUs [Member] | July 2016 Grant Date [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Performance period	3 years
Market-based PSUs [Member] | Minimum [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Percentage of performance to be achieved	50.00%
Market-based PSUs [Member] | Maximum [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Percentage of performance to be achieved	200.00%
Performance-Based PSUs [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Unvested restricted stock and stock units outstanding	55,330	192,310
Unamortized compensation expense	$ 1,800,000
Weighted-average period for unamortized compensation cost expected to be recognized	1 year
Non-vested shares			55,330
Aggregate intrinsic value of restricted stock outstanding	$ 3,000,000	$ 2,000,000	$ 2,200,000
Share-based compensation	$ 0	$ 0	$ 0