Fair Value Measurements Fair Value Measurements - Liabilities Not Measured at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
5% Convertible Senior Notes due 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stated interest rate (in hundredths)	5.00%
2% Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stated interest rate (in hundredths)	2.00%
Senior Notes | 5.75% Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stated interest rate (in hundredths)	5.75%
9% Debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stated interest rate (in hundredths)	9.00%
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Line of credit	$ 150,000
FHLB Advance	155,000	$ 155,000
5% Notes	144,948	144,789
2% Notes	204,900	204,672
5.75% Notes	417,695	417,406
9% Debentures	256,872	256,872
Total financial liabilities	1,329,415	1,178,739
Fair Value | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Line of credit	150,000
FHLB Advance	152,757	151,905
5% Notes	145,051	147,679
2% Notes	302,165	308,605
5.75% Notes	448,906	445,987
9% Debentures	332,436	323,040
Total financial liabilities	$ 1,531,315	$ 1,377,216