Long Term Debt (Details) (USD $)	9 Months Ended			9 Months Ended		3 Months Ended	9 Months Ended
	Sep. 30, 2014	Jun. 10, 2014	Dec. 31, 2013	Sep. 30, 2014 Senior Notes [Member]	Jul. 26, 2012 Senior Notes [Member]	Sep. 30, 2014 Convertible Debt Securities [Member]	Sep. 30, 2014 Convertible Debt Securities [Member]	Jun. 10, 2014 Convertible Debt Securities [Member]
Debt Instrument [Line Items]
Debt Instrument, Issuance Date				Jul. 26, 2012			Jun. 10, 2014
Debt Instrument, Face Amount				$ 250,000,000		$ 402,500,000	$ 402,500,000
Debt Instrument, Interest Rate, Stated Percentage				8.00%		3.25%	3.25%
Debt Instrument, Maturity Date				Aug. 01, 2020			Jun. 15, 2029
Proceeds from Debt, Net of Issuance Costs				245,000,000			391,400,000
Debt Instrument, Unamortized Discount				3,900,000	5,000,000	57,100,000	57,100,000	59,000,000
Debt Instrument, Convertible, Remaining Discount Amortization Period							6 years 9 months
Debt Issuance Cost							11,700,000
Unamortized Debt Issuance Expense				1,100,000		9,700,000	9,700,000
Interest Expense, Debt						5,300,000
Debt Instrument, Frequency of Periodic Payment				semi-annually			semiannually
Debt Instrument, Date of First Required Payment				Feb. 01, 2013			Dec. 15, 2014
Debt Instrument, Convertible, Carrying Amount of Equity Component		37,700,000
Debt Instrument, Call Date, Earliest				Aug. 01, 2016
Long-term Debt	591,464,000		245,670,000	246,055,000		345,409,000	345,409,000
Long-term Debt, Current Maturities	0
Total long-term debt, less current portion	591,464,000
Long-term Debt, Fair Value	678,300,000		283,300,000	273,300,000		405,000,000	405,000,000
Interest Paid	$ 20,000,000