Summary of Nonvested Restricted Shares Activity (Detail) (Restricted Stock, USD $)	12 Months Ended
	Dec. 31, 2013
Restricted Stock
NONVESTED NUMBER OF SHARES
Nonvested awards outstanding, beginning balance	152,100
Granted	98,900
Vested	(82,000)
Forfeited	(2,300)
Nonvested awards outstanding, ending balance	166,700
GRANT DATE FAIR VALUE
Nonvested awards outstanding, beginning balance	$ 43.68	[1]
Granted	$ 47.53	[1]
Vested	$ 42.88	[1]
Forfeited	$ 46.40	[1]
Nonvested awards outstanding, ending balance	$ 46.32	[1]

[1] Weighted Average