Stock Based Compensation - Additional Information (Detail) (USD $)	12 Months Ended							12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 1996 Non-Employee Director Stock Option Plan	Dec. 31, 2012 1994 Long-Term Incentive Plan	Dec. 31, 2012 2004 Long-Term Incentive Plan	Jul. 31, 2011 2004 Long-Term Incentive Plan	Mar. 31, 2010 2004 Long-Term Incentive Plan	Dec. 31, 2012 2006 Employee Stock Purchase Plan	Dec. 31, 2012 Stock Options	Dec. 31, 2011 Stock Options	Dec. 31, 2010 Stock Options	Dec. 31, 2012 RSUs	Dec. 31, 2011 RSUs	Dec. 31, 2010 RSUs	Dec. 31, 2012 RSUs Corporate Incentive Compensation Plan	Dec. 31, 2012 Employees Stock Compensation Plan	Dec. 31, 2012 Non-Employee Members Stock Compensation Plan	Dec. 31, 2012 Minimum	Dec. 31, 2012 Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option term	10 years
Maximum stock-based compensation arrangement vesting period, in years																		4 years	5 years
Compensation percentage of target incentive compensation eligible to be elected and received by employees															50.00%
Percentage on date of grant of equity amount for elected employees on target incentive compensation															50.00%
Vesting percentage of awards for elected employees of target incentive compensation															100.00%
Number of shares outstanding	3,897,000	2,532,000	50,000	80,000	4,333,000			500,000
Number of authorized shares						5,000,000
Value of common stock grantable to employees gross of fair market value of common stock adjustments on date of grant							$ 70,000
Stock price percentage of fair market value								85.00%
Stock purchase price percentage on completion date of offering period								95.00%
Aggregate number of shares issued under plan								119,000
Shares remaining for issuance for future equity grants	4,118,000				3,736,000			382,000
Shares granted																384,000	12,000
Weighted-average grant-date fair value of options granted									$ 9.43	$ 11.91	$ 12.22
Aggregate intrinsic value of options exercised									8,500,000	19,400,000	23,800,000
Closing price of common stock									$ 22.68			$ 22.68
Unrecognized stock-based compensation expense									13,300,000			5,900,000
Weighted-average period of recognition of unrecognized stock-based compensation expense (in years)									2 years 7 months 6 days			2 years 11 days
Weighted-average grant-date fair value of stock units granted												$ 32.35	$ 30.87	$ 33.90
Stock units, period of vesting												5 years
Vesting percentage of stock units within one year												20.00%
Vesting percentage of stock units within four years following year one												80.00%
Issued to employees															52,000
Vesting percentage of stock units															100.00%
RSU expected vesting date															March 2013
Restricted stock units, fair value												$ 7,100,000	$ 6,400,000	$ 4,500,000