Share-based Compensation - Summary of Stock Option Activity (Detail) (USD $)	1 Months Ended	12 Months Ended
	Sep. 06, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule Of Stock Option Activity [Line Items]
Non-vested stock Options, Balance, beginning of year		412,943	447,693	518,275
Options Outstanding, Granted				62,475
Options Outstanding, Exercised	(18,333)	(28,999)	(14,000)	(16,408)
Options Outstanding, Forfeited or expired		(16,038)	(20,750)	(116,649)
Non-vested stock Options, Balance, end of year		367,906	412,943	447,693
Option Outstanding, Options exercisable, end of year		312,020	295,168	249,177
Weighted Average Exercise Price, Balance, beginning of year		$ 13.74	$ 13.61	$ 13.85
Weighted Average Exercise Price, Granted				$ 11.30
Weighted Average Exercise Price, Exercised		$ 6.83	$ 6.38	$ 6.37
Weighted Average Exercise Price, Forfeited or expired		$ 16.86	$ 15.81	$ 14.46
Weighted Average Exercise Price, Balance, end of year		$ 14.15	$ 13.74	$ 13.61
Weighted Average Exercise Price, Options exercisable, end of year		$ 14.60	$ 14.36	$ 14.15