Stock-Based Compensation - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended				3 Months Ended	9 Months Ended		6 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 OptionPlan	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 Options and Restricted Stock	Sep. 30, 2012 Two Thousand Twelve Incentive Plan	Sep. 30, 2012 Two Thousand Twelve Incentive Plan	Sep. 30, 2012 Stock Options	Jun. 30, 2012 Two Thousand Six Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant						18,987,673			11,040
Shares transferred								1,030,673
Restricted shares granted			2,083,425				43,000			2,040,425
Restricted shares granted, weighted average grant date fair value			$ 12.78				$ 12.53			$ 12.78
Restricted shares granted, vesting period							5 years			5 years
Compensation cost related to restricted stock grants	$ 5,100,000	$ 4,200,000	$ 15,514,000	$ 12,096,000
Unrecognized compensation cost relating to unvested restricted stock	55,400,000		55,400,000
Unrecognized compensation cost relating to unvested restricted stock, recognition period (in years)			3 years 3 months 18 days
Stock Option Plans expiration period from the date of grant			10 years
Number of Stock Option Plans			8
Stock options outstanding	2,678,702		2,678,702		9,006,944
Intrinsic value of stock options outstanding and exercisable	204,000		204,000
Intrinsic values of options exercised			$ 0	$ 1,900,000