Long Term Debt (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Dec. 31, 2015	Jun. 10, 2014	Jul. 26, 2012
Debt Instrument [Line Items]
Unamortized Debt Issuance Expense	$ (8,469)	$ (9,149)
Long-term Debt	596,813	592,037
Long-term Debt, Current Maturities	0	0
Total long-term debt, less current portion	596,813	592,037
Long-term Debt, Fair Value	$ 726,400	790,500
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				$ 5,000
Debt Instrument, Frequency of Periodic Payment	semi-annually
Debt Instrument, Call Date, Earliest	Aug. 01, 2016
Long-term Debt	$ 247,048	246,750
Long-term Debt, Fair Value	$ 273,900	262,200
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			$ 59,000
Debt Instrument, Convertible, Remaining Discount Amortization Period	4 years 11 months 16 days
Debt Instrument, Frequency of Periodic Payment	semiannually
Long-term Debt	$ 358,234	354,436
Long-term Debt, Fair Value	$ 452,500	$ 528,300
Convertible Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Convertible, Carrying Amount of Equity Component			$ 37,700