Fair Value Measurements Fair Value Measurements - Liabilities Not Measured at Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
FHLB Advance due 2023	$ 160,025
Convertible Senior Notes due 2017	150,070	$ 345,616
Convertible Senior Notes due 2020	554,670	701,955
Convertible Junior Subordinated Debentures due 2063	285,244	455,067
Total Debt	1,150,009	1,502,638
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
FHLB Advance due 2023	155,000
Convertible Senior Notes due 2017	144,470	331,546
Convertible Senior Notes due 2020	491,854	490,755
Convertible Junior Subordinated Debentures due 2063	256,872	389,522
Total Debt	$ 1,048,196	$ 1,211,823