Activity in Management Stock Purchase Program (Detail) (Management Stock Purchase Plan, USD $)	12 Months Ended
	Dec. 31, 2013
Management Stock Purchase Plan
Share Based Compensation [Line Items]
Number of shares outstanding, beginning balance	212,167
Number of shares, purchased	51,524
Number of shares, vested	(50,300)
Number of shares, forfeited	(6,928)
Number of shares outstanding, ending balance	206,463
Weighted average grant date fair value outstanding, beginning balance	$ 30.76
Weighted average grant date fair value, purchased	$ 36.34
Weighted average grant date fair value, vested	$ 33.17
Weighted average grant date fair value, forfeited	$ 31.87
Weighted average grant date fair value outstanding, ending balance	$ 31.53