Stockholders' Equity (Details 2) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Stock options activity
Exercised (in shares)	(246,401)	(20,135)	(386,515)	(820,572)
Stock Options
Stock options activity
Outstanding at the beginning of the period (in shares)			4,923,377
Exercised (in shares)			(373,457)
Forfeited (in shares)			(3,858)
Outstanding at the end of the period (in shares)	4,546,062		4,546,062
Exercisable at the end of the period (in shares)	4,546,062		4,546,062
Stock options, Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)			36.98
Exercised (in dollars per share)			25.31
Forfeited (in dollars per share)			6.95
Outstanding at the end of the period (in dollars per share)	37.96		37.96
Exercisable at the end of the period, Weighted-Average Exercise Price (in dollars per share)	37.96		37.96
Stock options, Weighted Average Remaining Contractual Term
Outstanding at the end the period			5 years 2 months 12 days
Awards exercisable at the end of the period			5 years 2 months 12 days
Stock options, Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars)	85,436		85,436
Exercisable at the end of the period, Aggregate Intrinsic Value	85,436		85,436