Stockholders' Equity - Additional Information (Detail) (USD $)	6 Months Ended								1 Months Ended		3 Months Ended	1 Months Ended	3 Months Ended	6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2012 1.875% Convertible Notes	Dec. 31, 2011 1.875% Convertible Notes	Jun. 20, 2007 1.875% Convertible Notes	Jun. 30, 2012 2.50% Convertible Notes	Mar. 31, 2012 2.50% Convertible Notes	Dec. 31, 2011 2.50% Convertible Notes	May 23, 2011 2.50% Convertible Notes	Aug. 13, 2009 Stock Incentive Plan 2009	Jun. 30, 2012 Stock Incentive Plan 2009	Jun. 30, 2012 Amended and Restated Stock Incentive Plan 2009	Oct. 27, 2011 Stock Repurchase Program	Jun. 30, 2012 Stock Repurchase Program	Jun. 30, 2012 Stock Repurchase Program	Jun. 30, 2011 Stock Options	Jun. 30, 2012 Restricted Stock	Jun. 30, 2011 Restricted Stock	Jun. 30, 2012 Restricted Stock	Jun. 30, 2011 Restricted Stock	Jun. 30, 2012 Minimum	Jun. 30, 2012 Maximum
Class of Stock [Line Items]
Number of common stock shares authorized under Equity Incentive Plan									3,000,000		7,000,000
Plan expiration date									Aug. 13, 2019		Aug. 15, 2022
Number of additional common stock shares approved for issuance under amended and restated 2009 Equity Incentive Plan											4,000,000
Shareholders annual meeting date											Aug. 15, 2022
Common stock reserved for issuance										23,947
Repurchase of common stock authorized value												$ 200,000,000
Period of common stock repurchase, years												3 years
Repurchase of common stock, shares													3,207,750	5,237,468
Repurchase of common stock, value	85,062,000												50,000,000	85,100,000
Stock repurchase, remaining available amount														95,200,000
Options grant, expected life	7 years																			5 years	10 years
Debt instrument, interest rate, stated percentage		1.875%	1.875%	1.875%	2.50%	2.50%	2.50%	2.50%
Compensation expense related to stock grants															200,000	2,600,000	2,500,000	5,200,000	4,800,000
Compensation cost not yet recognized																12,100,000		12,100,000
Compensation cost not yet recognized, period for recognition																		4 years
Restricted common stock, value of shares withheld																$ 300,000	$ 400,000	$ 400,000	$ 2,200,000