Stock-Based Compensation - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period	1 year 4 months 24 days
Total unrecognized compensation cost	$ 1,900,000
2011 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of common stock available under the 2011 plan	4,000,000
2001 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
2001 Equity Incentive Plan	Mar. 14, 2011
Stock Appreciation Rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation plan expiration	10 years
Share-based compensation vesting period	One-third on each of the first three anniversaries of the date of grant
Restricted Shares And Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation vesting period	One-third on each of the first three anniversaries of the date of grant
Weighted average period	1 year 6 months
Total unrecognized compensation cost	15,000,000
Restricted Shares And Restricted Stock Units | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of vesting possibilities	0.00%
Restricted Shares And Restricted Stock Units | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of vesting possibilities	100.00%
Common Stock Units and Share Awards under 2004 Non Employee Director Fee Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period	3 months 18 days
Total unrecognized compensation cost	300,000
Value of initial granted shares of common stock to new non employee director	60,000
Vesting period of initial granted shares of common stock to new non employee director	Twelve equal quarterly installments, one-twelfth on the date of grant and an additional one-twelfth on each successive third monthly anniversary of the date of grant
Previous value of annual retainer to new non employee director	95,000
Amended annual retainer payable in cash to new non employee director	50,000
Amended value of annual retainer to new non employee director	125,000
Amended vesting period of cash annual retainer to non-employee chairman and committee members	Vests in four equal quarterly installments, one-fourth on the day following the annual meeting of shareholders, and an additional one-fourth on each successive third monthly anniversary of the date of grant
Vesting period of annual granted shares of common stock to non-employee director	Vests in eight equal quarterly installments, one-eighth on the day following the annual meeting of shareholders, and an additional one-eighth on each successive third monthly anniversary of the date of grant
Increased stock component of annual retainer	30,000
Share-based compensation arrangement by share-based payment award, amended vesting period	1 year
Vesting period for the annual equity award, before amendment	2 years
Amended vesting period of annual granted shares of common stock to non-employee director	Four equal quarterly installments, one-fourth on the date of grant and an additional one-fourth on each successive third monthly anniversary of the date of grant
Number of common stock equivalent to common stock unit	1
Deferred Compensation, Share-based Payments
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period	3 years
Total unrecognized compensation cost	100,000
Percentage of contribution in respect of amounts deferred by certain senior management participants	50.00%
Vesting period of matching contributions and associated earnings	Over seven year service period
Accrued employee compensation and benefits	5,100,000	4,200,000
Common stock match associated with the deferred compensation plan carrying value	1,400,000	1,200,000
Deferred Compensation, Share-based Payments | President And Senior Vice Presidents [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Amounts deferred by certain senior management personnel	12,000
Deferred Compensation, Share-based Payments | Vice President [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Amounts deferred by certain senior management personnel	$ 7,500