Benefit Plans - Options Outstanding and Options Exercisable by Exercise Price with Weighted-Average Remaining Contractual Life for Options Outstanding and Weighted-Average Exercise Price (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014
Exercise Price 15-20 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range Limit	$ 15
Exercise Price Upper Range Limit	$ 20
Options Outstanding, Number	149,700
Options Outstanding, Weighted-Average Remaining Contractual Life (Years)	1 year 2 months 1 day
Options Outstanding, Weighted-Average Grant Date Value	$ 15.62
Options Exercisable, Number	149,700
Options Exercisable, Weighted-Average Grant Date Value	$ 15.62
Exercise Price 20-25 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range Limit	$ 20
Exercise Price Upper Range Limit	$ 25
Options Outstanding, Number	229,225
Options Outstanding, Weighted-Average Remaining Contractual Life (Years)	1 year 9 months 14 days
Options Outstanding, Weighted-Average Grant Date Value	$ 23.19
Options Exercisable, Number	212,040
Options Exercisable, Weighted-Average Grant Date Value	$ 23.18
Exercise Price 25-30 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range Limit	$ 25
Exercise Price Upper Range Limit	$ 30
Options Outstanding, Number	653,435
Options Outstanding, Weighted-Average Remaining Contractual Life (Years)	2 years 6 months 21 days
Options Outstanding, Weighted-Average Grant Date Value	$ 29.12
Options Exercisable, Number	510,465
Options Exercisable, Weighted-Average Grant Date Value	$ 29.24
Exercise Price 30-35 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range Limit	$ 30
Exercise Price Upper Range Limit	$ 35
Options Outstanding, Number	302,000
Options Outstanding, Weighted-Average Remaining Contractual Life (Years)	5 years 6 months 21 days
Options Outstanding, Weighted-Average Grant Date Value	$ 32.35
Options Exercisable, Number	10,400
Options Exercisable, Weighted-Average Grant Date Value	$ 32.40
Exercise Price 35-40 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range Limit	$ 35
Exercise Price Upper Range Limit	$ 40
Options Outstanding, Number	9,400
Options Outstanding, Weighted-Average Remaining Contractual Life (Years)	5 years 11 months 15 days
Options Outstanding, Weighted-Average Grant Date Value	$ 37.83
Options Exercisable, Number	1,000
Options Exercisable, Weighted-Average Grant Date Value	$ 38.89
Exercise Price 15-40 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range Limit	$ 15
Exercise Price Upper Range Limit	$ 40
Options Outstanding, Number	1,343,760
Options Outstanding, Weighted-Average Remaining Contractual Life (Years)	2 years 11 months 19 days
Options Outstanding, Weighted-Average Grant Date Value	$ 27.25
Options Exercisable, Number	883,605
Options Exercisable, Weighted-Average Grant Date Value	$ 25.37