Share Based Compensation - Summarized Activity of Cash-Settled Stock Appreciation Rights (Detail) (Stock Appreciation Rights (SARs) [Member], USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Stock Appreciation Rights (SARs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value		$ 11.38
Balance at beginning of year	866,000
Granted, Rights Outstanding	0
Exercised, Rights Outstanding	(265,000)
Forfeited, Rights Outstanding	0
Balance at end of period	601,000
Exercisable at end of period, Rights Outstanding	554,000
Granted, Weighted Average Grant Date Fair Value	$ 0
Exercised, Weighted Average Exercise Price	$ 10.23
Forfeited, Weighted Average Grant Date Fair Value	$ 0
Balance at end of period, Weighted Average Exercise Price	$ 11.88
Exercisable at end of period, Weighted Average Exercise Price	$ 11.38
Balance at beginning of year, Weighted Average Remaining Contractual Term	6 years	6 years
Exercisable at end of period, Weighted Average Remaining Contractual Term	6 years
Balance at beginning of year, Aggregate Intrinsic Value	$ 5,256
Balance at end of period, Aggregate Intrinsic Value	5,797
Exercisable at end of period, Aggregate Intrinsic Value	$ 5,623