Investments (Details Textual) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Investments (Textual) [Abstract]
Fair value of issued securities	$ 6,893,090	$ 6,009,573
Investments (Additional Textual) [Abstract]
Fair value of securities transferred	0	24,791
Obligation for securities sold under agreement to repurchase, including accrued interest	0	25,864
Cash received in an amount equal to fair value of securities transferred	95.00%
Federal Home Loan Bank Funding Agreements	500,000	250,000
Investment Grade Rate	80.00%
Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Investments (Textual) [Abstract]
Fair value of issued securities	302,222	336,193
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
Investments (Textual) [Abstract]
Fair value of issued securities	432,432	427,172
Government National Mortgage Association Certificates and Obligations (GNMA) [Member]
Investments (Textual) [Abstract]
Fair value of issued securities	137,867	126,245
Federal Home Loan Bank [Member] | Fixed Maturities [Member]
Investments (Additional Textual) [Abstract]
Securities Deposited Fair Value	18,361	17,967
Securities Deposited As Collateral	$ 539,235	$ 274,437