Investments Investments in Any One Issuer Exceeding Ten Percent of Equity (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Concentration Risk [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 1,084,105	$ 826,858
Available-for-sale Securities	1,084,510	$ 829,993
Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Available-for-sale Securities, Amortized Cost Basis	755,418
Available-for-sale Securities	$ 750,684
Stockholders' Equity, Total [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	10.00%
Government National Mortgage Association Certificates and Obligations (GNMA) [Member] \| Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 111,340
Available-for-sale Securities	109,627
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member] \| Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Available-for-sale Securities, Amortized Cost Basis	171,582
Available-for-sale Securities	171,450
Federal Home Loan Bank Certificates and Obligations (FHLB) [Member] \| Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Available-for-sale Securities, Amortized Cost Basis	103,806
Available-for-sale Securities	103,251
Federal National Mortgage Association Certificates and Obligations (FNMA) [Member] \| Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Available-for-sale Securities, Amortized Cost Basis	368,690
Available-for-sale Securities	$ 366,356

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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