Investments and Fair Value Measurements Fair Value Inputs, Quantitative Information (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Warrants	$ 2,342	$ 1,935
Fair value of derivatives embedded within convertible debt	169,386	112,062
Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Warrants	2,342	1,935
Fair value of derivatives embedded within convertible debt	169,386	112,062
Option Model [Member] | Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Warrants	2,342	1,935
Discounted Cash Flow [Member] | Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fair value of derivatives embedded within convertible debt	$ 169,386	$ 112,062
Warrant [Member] | Option Model [Member] | Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Stock price (dollars per share)	$ 3.95	$ 3.13
Exercise price (dollars per share)	$ 1.68	$ 1.68
Term (in years)	1 year 10 months 2 days	2 years 9 months 18 days
Volatility	44.42%	53.82%
Dividend rate	0.00%	0.00%
Risk-free return	0.70%	0.72%
Derivative Financial Instruments, Liabilities [Member] | Discounted Cash Flow [Member] | Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Stock price (dollars per share)	$ 21.31	$ 16.37
Volatility	16.00%	18.00%
Assumed annual stock dividend	5.00%	5.00%
Assumed annual cash dividend (dollars per share)	$ 1.60	$ 1.60
Convertible trading price	106.80%	118.70%
Implied credit spread	6.75%
Discount rate		8.00%
Minimum [Member] | Derivative Financial Instruments, Liabilities [Member] | Discounted Cash Flow [Member] | Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Implied credit spread	6.25%
Discount rate		7.50%
Maximum [Member] | Derivative Financial Instruments, Liabilities [Member] | Discounted Cash Flow [Member] | Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Implied credit spread	7.25%
Discount rate		8.50%