Investments and Fair Value Measurements Fair Value Inputs, Quantitative Information (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fair value of derivatives embedded within convertible debt	$ 144,042	$ 169,386
Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fair value of derivatives embedded within convertible debt	144,042	169,386
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	$ 144,042	$ 169,386
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)	$ 23.59	$ 21.31
Volatility	18.30%	16.00%
Assumed annual stock dividend	5.00%	5.00%
Assumed annual cash dividend (dollars per share)	$ 1.60	$ 1.60
Convertible trading price	114.31%	106.80%
Implied credit spread	5.25%
Discount rate		6.75%
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	5.00%
Discount rate		6.25%
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	5.50%
Discount rate		7.25%