SARs Outstanding (Detail) (Stock appreciation rights, USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Stock appreciation rights
SARs
Beginning balance	16,500	52,000	59,250
Granted
Exercised	(16,500)	(35,500)	(7,250)
Expired or forfeited
Ending balance		16,500	52,000
Number of SARs exercisable		16,500	52,000
Average Exercise Prices
Beginning balance	$ 18.74	$ 14.05	$ 13.89
Granted
Exercised	$ 18.74	$ 11.86	$ 12.76
Expired or forfeited
Ending balance		$ 18.74	$ 14.05
Number of SARs exercisable		$ 18.74	$ 14.05