Stock-Based Compensation - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014 plan	Dec. 31, 2013	Dec. 31, 2012	Mar. 20, 2007
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of incentive plans	2
Options, Granted (in shares)	71,000
Weighted-average fair value of grants (in dollars per share)	$ 12.62
Options vested	611,977
Weighted average exercise price	$ 19.02
Aggregate intrinsic value	$ 3,800,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	4 years 2 months 12 days
Vesting percentage in year one	33.00%
Vesting percentage in year two	33.00%
Vesting percentage in year three	34.00%
Options exercisable (in shares)	288,412
Options, Exercisable, Weighted average exercise price	$ 18.61
Option exercisable, Weighted average remaining contractual term	3 years 2 months 9 days
Option exercisable, aggregate intrinsic value	1,925,000
Cash received from the exercise of options	2,300,000	8,800,000	0
Tax benefits realized for the tax deductions from options exercised	400,000	1,000,000	0
Aggregate intrinsic value of stock options exercised	1,000,000	2,600,000	0
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, Granted (in shares)	71,000	190,500	222,100
Weighted-average fair value of grants (in dollars per share)	$ 12.62	$ 10.95	$ 4.95
Option vesting term	4 years
Unrecognized compensation cost related to stock option	2,400,000
Weighted average period	2 years 4 months 24 days
Allocated Share-based Compensation Expense	1,500,000	1,200,000	1,100,000
Total fair value of options expensed before tax benefits	1,300,000	1,100,000	1,300,000
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option vesting term	3 years
Weighted average period	1 year 9 months 18 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value	1,300,000	1,100,000	600,000
Tax benefit realized on vesting of options	500,000	400,000	300,000
Awards, Granted (in shares)	86,300	65,550	73,900
Granted, Weighted Average Grant Date Fair Value (in dollars per share)	$ 24.74	$ 18.75	$ 13.18
Allocated Share-based Compensation Expense	1,300,000	900,000	700,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options	1,600,000
Performance Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period	1 year 3 months 18 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value	100,000	0	100,000
Awards, Granted (in shares)	67,500	85,500	82,500
Granted, Weighted Average Grant Date Fair Value (in dollars per share)	$ 24.90	$ 16.15	$ 13.04
Allocated Share-based Compensation Expense	1,000,000	300,000	600,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options	$ 1,500,000
2007 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance	4,198			1,200,000
Shares reserved for future issuance other than stock options				400,000
2013 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance	19,800			240,000