Long Term Debt (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Jun. 10, 2014	Jul. 26, 2012
Debt Instrument [Line Items]
Debt Instrument, Convertible, Carrying Amount of Equity Component			$ 37,700
Long-term Debt	$ 599,183	$ 593,350
Long-term Debt, Current Maturities	0
Total long-term debt, less current portion	599,183
Long-term Debt, Fair Value	736,900	$ 711,100
Interest Paid	$ 26,500
Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Issuance Date	Jul. 26, 2012
Debt Instrument, Face Amount	$ 250,000
Debt Instrument, Interest Rate, Stated Percentage	8.00%
Debt Instrument, Maturity Date	Aug. 01, 2020
Proceeds from Debt, Net of Issuance Costs	$ 245,000
Debt Instrument, Unamortized Discount	3,400			$ 5,000
Unamortized Debt Issuance Expense	$ 1,000
Debt Instrument, Frequency of Periodic Payment	semi-annually
Debt Instrument, Date of First Required Payment	Feb. 01, 2013
Debt Instrument, Call Date, Earliest	Aug. 01, 2016
Long-term Debt	$ 246,605
Long-term Debt, Fair Value	$ 261,800
Convertible Debt Securities [Member]
Debt Instrument [Line Items]
Debt Instrument, Issuance Date	Jun. 10, 2014
Debt Instrument, Face Amount	$ 402,500
Debt Instrument, Interest Rate, Stated Percentage	3.25%
Debt Instrument, Maturity Date	Jun. 15, 2029
Proceeds from Debt, Net of Issuance Costs	$ 391,400
Debt Instrument, Unamortized Discount	$ 49,900		$ 59,000
Debt Instrument, Convertible, Remaining Discount Amortization Period	5 years 8 months 16 days
Debt Issuance Cost	$ 11,700
Unamortized Debt Issuance Expense	$ 8,500
Debt Instrument, Frequency of Periodic Payment	semiannually
Long-term Debt	$ 352,578
Long-term Debt, Fair Value	$ 475,100