Share Based Compensation - Summarized Activity of Stock Option Awards (Detail) (USD $)				12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Stock Options [Member]	Dec. 31, 2011 Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Balance at beginning of year, Options Outstanding				1,284,000
Granted, Options Outstanding				473,000
Exercised, Options Outstanding
Forfeited, Options Outstanding				(1,000)
Balance at end of period, Options Outstanding				1,756,000	1,284,000
Exercisable at end of period, Options Outstanding				975,000
Balance at beginning of year, Weighted Average Exercise Price				$ 22.22
Granted, Weighted Average Exercise Price				$ 15.94
Exercised, Weighted Average Exercise Price
Forfeited, Weighted Average Exercise Price				$ 16.89
Balance at end of period, Weighted Average Exercise Price				$ 20.53	$ 22.22
Exercisable at end of period, Weighted Average Exercise Price				$ 23.66
Weighted Average Remaining Contractual Term				7 years	7 years
Exercisable at end of period, Weighted Average Remaining Contractual Term				6 years
Balance at beginning of period, Aggregate Intrinsic Value				$ 944,000
Balance at end of period, Aggregate Intrinsic Value				1,956,000	944,000
Exercisable at end of period, Aggregate Intrinsic Value	$ 64,000	$ 766,000	$ 578,000	$ 1,079,000