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	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
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, Outstanding, Weighted Average Remaining Contractual Terms	4 years	5 years
Balance at beginning of year	580,000	866,000
Granted, Rights Outstanding	0
Exercised, Rights Outstanding	(116,000)
Forfeited, Rights Outstanding	(6,000)
Balance at end of period	458,000	580,000
Exercisable at end of period, Rights Outstanding	458,000
Non-vested at beginning of year, Weighted Average Grant Date Fair Value	$ 11.96	$ 11.38
Granted, Weighted Average Exercise Price	$ 0.00
Exercised, Weighted Average Exercise Price	$ 9.41
Forfeited, Weighted Average Grant Date Fair Value	$ 17.80
Non-vested at end of period, Weighted Average Grant Date Fair Value	$ 12.54	$ 11.96
Exercisable at end of period, Weighted Average Exercise Price	$ 12.54
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Exercisable Weighted Average Remaining Contractual Term	4 years
Aggregate Intrinsic Value	$ 1,732	$ 5,400
Exercisable at end of period, Aggregate Intrinsic Value	$ 1,732