Investments (Details Textual) - USD ($) $ in Thousands		Jun. 30, 2015	Dec. 31, 2014
Investments (Textual) [Abstract]
Fair value of issued securities	[1]	$ 6,897,058	$ 6,893,090
Investments (Additional Textual) [Abstract]
Federal Home Loan Bank Funding Agreements		$ 500,000	500,000
Investment Grade Rate		82.00%
Federal Home Loans Bank Of Chicago [Member]
Investments (Textual) [Abstract]
Fair value of issued securities		$ 537,865	539,235
Governmental Agencies as Required by Law in Various States [Member]
Investments (Textual) [Abstract]
Fair value of issued securities		18,377	18,361
Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Investments (Textual) [Abstract]
Fair value of issued securities		252,549	302,222
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
Investments (Textual) [Abstract]
Fair value of issued securities		435,304	432,432
Government National Mortgage Association Certificates and Obligations (GNMA) [Member]
Investments (Textual) [Abstract]
Fair value of issued securities		$ 136,356	$ 137,867

[1] Fair value includes securities issued by Federal National Mortgage Association (“FNMA”) of $252,549 and $302,222; Federal Home Loan Mortgage Corporation (“FHLMC”) of $435,304 and $432,432; and Government National Mortgage Association (“GNMA”) of $136,356 and $137,867 as of June 30, 2015 and December 31, 2014, respectively.