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Fair Value Measurements (Carrying Value and Estimated Fair Value of Financial Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Held-to-maturity Securities	$ 201,354	$ 318,137
Available-for-sale Securities, Debt Securities	4,408,203	4,066,122
Equity securities, AFS	207,051	191,400
Short-term investments	194,819	131,972
Notes payable	388,192	372,689
Carrying Amount [Member]
Held-to-maturity Securities	201,354	318,137
Available-for-sale Securities, Debt Securities	4,408,203	4,066,122
Equity securities, AFS	207,051	191,400
Short-term investments	194,819	131,972
Notes payable	388,192	372,689
Carrying Amount [Member] | Zero Point Sixty Three Percent Borrowing From Federal Home Loan Bank Due July 22, 2016 [Member]
Notes payable	15,000	0
Carrying Amount [Member] | One Point Twenty Five Percent Borrowing From Federal Home Loan Bank [Member]
Notes payable	45,000	45,000
Carrying Amount [Member] | Seven Point Twenty Five Percent Senior Notes [Member]
Notes payable	49,898	49,896
Carrying Amount [Member] | Six Point Seventy Percent Senior Notes [Member]
Notes payable	99,415	99,401
Carrying Amount [Member] | Five Point Eight Hundred Seventy Five [Member]
Notes payable	185,000	185,000
Carrying Amount [Member] | Long Term Debt Excluding Issuance Costs [Member]
Notes payable	394,313	379,297
Carrying Amount [Member] | Unamortized Debt Issuance Costs [Member]
Notes payable	(6,121)	(6,608)
Fair Value [Member]
Held-to-maturity Securities	209,544	333,961
Available-for-sale Securities, Debt Securities	4,408,203	4,066,122
Equity securities, AFS	207,051	191,400
Short-term investments	194,819	131,972
Notes payable	419,826	404,270
Fair Value [Member] | Zero Point Sixty Three Percent Borrowing From Federal Home Loan Bank Due July 22, 2016 [Member]
Notes payable	14,977	0
Fair Value [Member] | One Point Twenty Five Percent Borrowing From Federal Home Loan Bank [Member]
Notes payable	45,083	45,244
Fair Value [Member] | Seven Point Twenty Five Percent Senior Notes [Member]
Notes payable	56,929	59,181
Fair Value [Member] | Six Point Seventy Percent Senior Notes [Member]
Notes payable	110,363	114,845
Fair Value [Member] | Five Point Eight Hundred Seventy Five [Member]
Notes payable	$ 192,474	$ 185,000

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