Investments and Fair Value Measurements Fair Value Inputs, Quantitative Information (Details) - Fair Value, Measurements, Recurring - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value of derivatives embedded within convertible debt	$ 134,348	$ 144,042
Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value of derivatives embedded within convertible debt	134,348	144,042
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	$ 134,348	$ 144,042
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)	$ 22.84	$ 23.59
Volatility	18.61%	18.30%
Assumed annual stock dividend	5.00%	5.00%
Assumed annual cash dividend (dollars per share)	$ 1.60	$ 1.60
Convertible trading price	110.56%	114.30%
Implied credit spread	6.50%	5.25%
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	6.00%	5.00%
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	7.00%	5.50%