Investments Maturity Distribution of Debt Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Due in One Year or Less, Amortized Cost Basis	$ 30,664
Available-for-sale Securities, Debt Maturities, Due After One Year Through Five Years, Amortized Cost Basis	107,702
Available-for-sale Securities, Debt Maturities, Due After Five Years Through Ten Years, Amortized Cost Basis	182,804
Available-for-sale Securities, Debt Maturities, Due After Ten Years, Amortized Cost Basis	646,748
Available-for-sale Debt Securities, Amortized Cost Basis	967,918	$ 935,977
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Due in One Year or Less, Fair Value	30,737
Available-for-sale Securities, Debt Maturities, Due After One Year Through Five Years, Fair Value	111,166
Available-for-sale Securities, Debt Maturities, Due After Five Years Through Ten Years, Fair Value	185,086
Available-for-sale Securities, Debt Maturities, Due After Ten Years, Fair Value	649,462
Available-for-sale Debt Securities, Fair Value	976,451
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Held-to-maturity Securities, Debt Maturities, Due in One Year or Less, Amortized Cost Basis	9,126
Held-to-maturity Securities, Debt Maturities, Due After One Year Through Five Years, Amortized Cost Basis	41,986
Held-to-maturity Securities, Debt Maturities, Due After Five Years Through Ten Years, Amortized Cost Basis	49,031
Held-to-maturity Securities, Debt Maturities, Due After Ten Years, Amortized Cost Basis	114,371
Held-to-maturity securities	214,514	233,961
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Held-to-maturity Securities, Debt Maturities, Due in One Year or Less, Fair Value	9,137
Held-to-maturity Securities, Debt Maturities, Due After One Year Through Five Years, Fair Value	42,761
Held-to-maturity Securities, Debt Maturities, Due After Five Years Through Ten Years, Fair Value	49,612
Held-to-maturity Securities, Debt Maturities, Due After Ten Years, Fair Value	117,264
Fixed maturities held-to-maturity, fair value	218,774	241,377
Total Fixed Maturity Securities, Amortized Cost	1,182,432	1,169,938
Total Fixed Maturity Securities, Fair Value	$ 1,195,225	$ 1,215,986