Summary of Stock Appreciation Rights Activity (Detail) (Stock Appreciation Rights (SARs), USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Stock Appreciation Rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested shares, beginning balance	657
Granted, shares	259	215
Exercised, shares
Forfeited or expired, shares	(51)
Nonvested shares, ending balance	865
Vested or expected to vest, shares	865
Exercisable, shares	470
Non vested, weighted average exercise price, beginning balance
Granted, weighted average exercise price
Exercised, weighted average exercise price
Forfeited or expired, weighted average exercised price
Non vested, weighted average exercise price, ending balance
Vested or expected to vest, weighted average exercise price
Exercisable, weighted average exercise price
Non vested, weighted average remaining contractual term	7 years 6 months
Vested or expected to vest, weighted average remaining contractual term	7 years 6 months
Exercisable, weighted average remaining contractual term	6 years 3 months 18 days
Non vested, aggregate intrinsic value
Vested or expected to vest, aggregate intrinsic value
Exercisable, aggregate intrinsic value