Investments Maturity Distribution of Debt Securities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, within One Year, Amortized Cost Basis	$ 44,805
Available-for-sale Securities, Debt Maturities, after One through Five Years, Amortized Cost Basis	101,337
Available-for-sale Securities, Debt Maturities, after Five through Ten years, Amortized Cost Basis	123,319
Available-for-sale Securities, Debt Maturities, after Ten Years, Amortized Cost Basis	666,516
Available-for-sale Debt Securities, Amortized Cost Basis	935,977	$ 860,473
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, within One Year, Fair Value	45,049
Available-for-sale Securities, Debt Maturities, after One through Five Years, Fair Value	104,873
Available-for-sale Securities, Debt Maturities, after Five through Ten Years, Fair Value	131,125
Available-for-sale Securities, Debt Maturities, after Ten Years, Fair Value	693,562
Available for Sale Securities, Total	974,609
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Held-to-maturity Securities, Debt Maturities, within One Year, Net Carrying Amount	19,025
Held-to-maturity Securities, Debt Maturities, after One through Five Years, Net Carrying Amount	46,497
Held-to-maturity Securities, Debt Maturities, after Five through Ten Years, Net Carrying Amount	46,502
Held-to-maturity Securities, Debt Maturities, after Ten Years, Net Carrying Amount	121,937
Fixed maturities held-to-maturity, at amortized cost	233,961	247,004
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Held-to-maturity Securities, Debt Maturities, within One Year, Fair Value	19,123
Held-to-maturity Securities, Debt Maturities, after One through Five Years, Fair Value	48,014
Held-to-maturity Securities, Debt Maturities, after Five through Ten Years, Fair Value	48,436
Held-to-maturity Securities, Debt Maturities, after Ten Years, Fair Value	125,804
Held-to-maturity Securities, Fair Value	241,377	$ 252,545
Total Fixed maturity securities, Amortized Cost	1,169,938
Total Fixed Maturity Securities, Fair Value	$ 1,215,986
Number of investments exceeding 10% of stocksholder's equity	0
Number of Non-Income Producing Fixed Maturity Securities	0