Convertible Notes (Narrative) (Details) (USD $)					0 Months Ended	12 Months Ended		0 Months Ended		12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Convertible notes	Dec. 31, 2012 Convertible notes	Aug. 16, 2013 Convertible notes 1.125% Convertible Senior Notes due 2018	Dec. 31, 2013 Convertible notes 1.125% Convertible Senior Notes due 2018	Dec. 31, 2012 Convertible notes 1.125% Convertible Senior Notes due 2018	Jul. 10, 2009 Convertible notes 5% Convertible Senior Notes due 2014	Jun. 29, 2009 Convertible notes 5% Convertible Senior Notes due 2014	Dec. 31, 2013 Convertible notes 5% Convertible Senior Notes due 2014	Dec. 31, 2012 Convertible notes 5% Convertible Senior Notes due 2014	Dec. 31, 2011 Convertible notes 5% Convertible Senior Notes due 2014	Aug. 16, 2013 Convertible Senior Notes [Member] 1.125% Convertible Senior Notes due 2018
Debt Instrument [Line Items]
Face Value			$ 310,500,000	$ 172,500,000	$ 138,000,000	$ 138,000,000	$ 0		$ 150,000,000	$ 172,500,000	$ 172,500,000
Liability Component, Principal amount					107,700,000			14,300,000	92,400,000
Equity Component, Principal amount					30,300,000			8,200,000	57,600,000
Additional borrowings on debt instrument								22,500,000
Debt discount amortization period					5 years	56 months			5 years	6 months
Stated Interest rate (as a percent)					1.125%	1.125%			5.00%				1.125%
Debt Issuance Cost					3,600,000				5,100,000
Debt Issuance Cost, Convertible, Liability Component					2,800,000				3,200,000
Debt Issuance Cost, Convertible, Equity Component					800,000				1,900,000
Debt Instrument, Term					5 years				5 years
Periodic interest payment										8,600,000	8,600,000	8,600,000
Conversion rate, number of shares to be issued per $1000 of principal (in shares)					82.8329				51.8
Principal amount of notes used as the denominator to determine number of shares converted into notes					1,000				1,000
Initial conversion price of notes (in dollars per share)					$ 12.07				$ 19.31
Number of trading days within 30 consecutive trading days in which the closing price of the entity's common stock must exceed the conversion price for the notes to be redeemable, minimum					20 days				20 days
Number of consecutive trading days during which the closing price of the entity's common stock must exceed the conversion price for at least 20 days in order for the notes to be redeemable					30 days				30 days
Percentage of the closing sales price of the entity's common stock that the conversion price must exceed in order for the notes to be convertible					130.00%				130.00%
Number of business days immediately after any ten consecutive trading day period during the note measurement period					5 days				5 days
Number of consecutive trading days before the five business days during the debt instrument measurement period					5 days				10 days
Denomination of the principal amount of notes used to calculate the percent of trading price during the debt instrument measurement period					1,000				1,000
Maximum conversion price as a percentage of closing stock price					98.00%				98.00%
Number of trading days conversion reference period									20 days
Number of consecutive trading days during which the closing price of the entity's common stock must exceed the conversion price for at least 20 days in order for the notes to be redeemable at the company's option									30 days
Percentage of face amount of debt instrument redeemable at the company's option					100.00%				100.00%
Number of trading days within 30 consecutive trading days in which the closing price of the entity's common stock must exceed the conversion price for the notes to be redeemable at the company's option, minimum									20 days
Percentage of the closing sales price of the entity's common stock that the conversion price must exceed in order for the notes to be redeemable at the company's option									130.00%
Percentage of face amount which may be redeemed by the debt holder for cash upon occurrence of a fundamental change									100.00%
Maximum increase in conversion rate per $1000 principal amount upon occurrence of fundamental change									15.5401
Events of default
Period of default in payment of interest (in days)					30 days				30 days
Period of default to comply with other agreements (in days)					60 days				60 days
Minimum percentage of aggregate outstanding principal required for default event with other agreements					25.00%				25.00%
Minimum principal amount of debt nonpayment required for debt default to occur					40,000,000				30,000,000
Period of nonpayment of principal amount required for debt default to occur (in days)					30 days				10 days
Minimum percentage of aggregate outstanding principal required for nonpayment of debt default to occur					25.00%				25.00%
Minimum percentage of aggregate outstanding principal required for immediate payment declaration to occur					25.00%				25.00%
Additional paid in capital	$ 1,128,148,000	$ 1,075,761,000	$ 93,400,000	$ 63,900,000