Common Stock and Convertible Senior Subordinated Notes (Details) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	1 Months Ended		12 Months Ended
	Dec. 31, 2009	Feb. 28, 2009	Dec. 31, 2009
Convertible Senior Subordinated Notes due 2015
Shares issued (in shares)	13,000	10,000
Shares issued price (in dollars per share)	$ 38.50	$ 32.00
Net proceeds from issuance of common stock	$ 488,100,000	$ 313,300,000	$ 801,385,000
Underwriting discount	12,100,000	6,400,000
Other stock issuance expenses	$ 300,000	$ 300,000