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)	12 Months Ended
	Dec. 31, 2020 $ / shares shares
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 | shares	206,125
Options Outstanding, Weighted-Average Remaining Contractual Life (Years)	2 years 2 months 1 day
Options Outstanding, Weighted-Average Grant Date Value	$ 24.60
Options Exercisable, Number | shares	181,480
Options Exercisable, Weighted-Average Grant Date Value	$ 24.60
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 | shares	2,840
Options Outstanding, Weighted-Average Remaining Contractual Life (Years)	2 years 1 month 24 days
Options Outstanding, Weighted-Average Grant Date Value	$ 25.12
Options Exercisable, Number | shares	2,290
Options Exercisable, Weighted-Average Grant Date Value	$ 25.13
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 | shares	190,585
Options Outstanding, Weighted-Average Remaining Contractual Life (Years)	2 years 10 months 17 days
Options Outstanding, Weighted-Average Grant Date Value	$ 33.97
Options Exercisable, Number | shares	119,805
Options Exercisable, Weighted-Average Grant Date Value	$ 33.79
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 | shares	6,800
Options Outstanding, Weighted-Average Remaining Contractual Life (Years)	3 years
Options Outstanding, Weighted-Average Grant Date Value	$ 39.19
Options Exercisable, Number | shares	5,440
Options Exercisable, Weighted-Average Grant Date Value	$ 39.19
Exercise Price 40-45 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range Limit	40
Exercise Price Upper Range Limit	$ 45
Options Outstanding, Number | shares	3,060
Options Outstanding, Weighted-Average Remaining Contractual Life (Years)	3 years 8 months 1 day
Options Outstanding, Weighted-Average Grant Date Value	$ 40.37
Options Exercisable, Number | shares	680
Options Exercisable, Weighted-Average Grant Date Value	$ 40.37
Exercise Price 20-45 [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	$ 45
Options Outstanding, Number | shares	409,410
Options Outstanding, Weighted-Average Remaining Contractual Life (Years)	2 years 6 months 7 days
Options Outstanding, Weighted-Average Grant Date Value	$ 29.33
Options Exercisable, Number | shares	309,695
Options Exercisable, Weighted-Average Grant Date Value	$ 28.45