Convertible Senior Notes (Details Textuals) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010	Mar. 22, 2007
Convertible Senior Notes (Textuals) [Abstract]
Convertible senior notes principal outstanding	$ 260,000	$ 260,000		$ 260,000
Interest rate of convertible senior notes	2.00%	2.00%
Convertible senior notes issuance date		March 28, 2007
Convertible senior notes due date		May 15, 2012
Convertible senior notes carrying amount, current	251,432	251,432	0
Convertible senior notes carrying amount, long-term	0	0	245,750
Unamortized discount of debt instruments	8,568	8,568
Remaining amortization period of the unamortized discount (in months)	11	11
Initial conversion ratio		23.5114
Principle amount applied to initial conversion ratio	1	1
Conversion premium	32.50%	32.50%
Closing price of Company's common stock	$ 70.47	$ 70.47			$ 32.10
Conversion price per share	$ 42.53	$ 42.53
If-converted value per dollar above the conversion price	6,100	6,100
Average market price of the Company's common stock	$ 66.37	$ 60.54
Shares of common stock covered under convertible note hedge transaction	6,112,964	6,112,964
Shares of common stock covered under warrants	6,112,964	6,112,964
Strike price of warrants	$ 53.77	$ 53.77
If-settled value per dollar above the warrant exercise price	6,100	6,100
Amount by which the if-converted value exceeds its principle amount at the balance sheet date		170,781
Amount owed to Company under hedges in cash or shares of its common stock if notes are converted	170,781	170,781
Value of common stock owed to warrant holders if warrants are exercised	$ 102,086	$ 102,086
Shares of common stock owed to warrant holders if warrants are exercised	1,449,000	1,449,000