Share-based Compensation - Summary of Information on Activity on SARs Settled in Cash (Detail) (USD $)	1 Months Ended	12 Months Ended
	Sep. 06, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [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
Options Outstanding, Options exercisable, Balance, 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
Cash-settled SARs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested stock Options, Balance, beginning of year		230,607	250,229	272,711
Options Outstanding, Granted
Options Outstanding, Exercised
Options Outstanding, Forfeited or expired		(23,844)	(19,622)	(22,482)
Non-vested stock Options, Balance, end of year		206,763	230,607	250,229
Options Outstanding, Options exercisable, Balance, end of year		190,236	176,446	139,700
Weighted Average Exercise Price, Balance, beginning of year		$ 14.81	$ 14.78	$ 14.75
Weighted Average Exercise Price, Granted
Weighted Average Exercise Price, Exercised
Weighted Average Exercise Price, Forfeited or expired		$ 14.50	$ 14.45	$ 14.37
Weighted Average Exercise Price, Balance, end of year		$ 14.84	$ 14.81	$ 14.78
Weighted Average Exercise Price, Options exercisable, end of year		$ 15.09	$ 15.43	$ 15.75