Long-Term Debt (Details 6) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jun. 30, 2009
Long-Term Debt
Interest expense related to amortization of debt discount	$ 23,407,000	$ 20,523,000	$ 18,323,000
4.25% convertible senior notes due June 2014
Long-Term Debt
Principle amount of senior notes				355,000,000
Interest rate (as a percent)	4.25%	4.25%		4.25%
Initial conversion rate of debt instrument (Shares per USD)	0.0431951
Initial conversion price per common stock shares (in dollars per share)	$ 23.15
Amount by which value of shares converted exceeds principal	169,400,000
Amount of unamortized discount of notes	11,300,000	34,300,000		97,900,000
Recognized interest expense related to the contractual interest coupon	15,100,000	15,100,000	15,100,000
Interest expense related to amortization of debt discount	23,000,000	20,500,000	18,300,000
Effective interest rate (as a percent)	11.67%
Price per share of common stock for call options purchased (in dollars per share)	$ 23.15
Warrant exercise price (in dollars per share)	$ 32.67
Effective conversion price (in dollars per share)	$ 32.67
Debt instrument face amount for effective conversion price	$ 325,000,000