Stock-Based Compensation - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non vested shares restricted shares, vesting period		4 years
Accelerated vesting of restricted shares	300,000
Accelerated stock compensation expense	$ 6,200,000
Intrinsic value of options exercised			100,000	100,000
Stock option exercised			4,000	178,886
Proceeds from exercises of stock options			100,000	5,083,000
Tax benefit from stock options exercised			0	400,000
Weighted average grant date fair value of restricted shares		$ 16.30	$ 28.01	$ 27.86
Fair values of vested restricted stock and stock options		1,500,000	9,700,000	6,700,000
Unrecognized compensation cost related to non-vested restricted stock and stock option compensation		$ 100,000
Vested restricted stock awards		83,967
Restricted stock units granted		59,891
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested restricted stock awards		100,000
Market Condition Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value of restricted shares			$ 15.69
Performance period (in years)		3 years
Restricted stock units granted			23,192
2009 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance		1,500,000