Summary of Investments (Fair Value of Investments) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Fixed maturities:
Amortized Cost	$ 1,653,296	$ 1,761,289
Gross Unrealized Appreciation	51,086	11,844
Gross Unrealized Depreciation	1,063	23,645
Fair Value	1,703,319	1,749,488
U.S. Treasury
Fixed maturities:
Amortized Cost	28,937	27,632
Gross Unrealized Appreciation	177	6
Gross Unrealized Depreciation	42	220
Fair Value	29,072	27,418
U.S. government agency
Fixed maturities:
Amortized Cost	137,846	215,535
Gross Unrealized Appreciation	2,245	896
Gross Unrealized Depreciation	41	1,749
Fair Value	140,050	214,682
States, municipalities and political subdivisions | General obligations | Midwest
Fixed maturities:
Amortized Cost	86,696	94,806
Gross Unrealized Appreciation	2,674	1,091
Gross Unrealized Depreciation	0	685
Fair Value	89,370	95,212
States, municipalities and political subdivisions | General obligations | Northeast
Fixed maturities:
Amortized Cost	31,213	37,326
Gross Unrealized Appreciation	1,111	432
Gross Unrealized Depreciation	0	103
Fair Value	32,324	37,655
States, municipalities and political subdivisions | General obligations | South
Fixed maturities:
Amortized Cost	113,289	114,710
Gross Unrealized Appreciation	2,757	754
Gross Unrealized Depreciation	71	1,553
Fair Value	115,975	113,911
States, municipalities and political subdivisions | General obligations | West
Fixed maturities:
Amortized Cost	105,978	107,787
Gross Unrealized Appreciation	3,927	1,229
Gross Unrealized Depreciation	12	1,175
Fair Value	109,893	107,841
States, municipalities and political subdivisions | Special revenue | Midwest
Fixed maturities:
Amortized Cost	139,244	140,025
Gross Unrealized Appreciation	5,203	1,609
Gross Unrealized Depreciation	9	870
Fair Value	144,438	140,764
States, municipalities and political subdivisions | Special revenue | Northeast
Fixed maturities:
Amortized Cost	62,469	62,737
Gross Unrealized Appreciation	2,232	452
Gross Unrealized Depreciation	0	1,241
Fair Value	64,701	61,948
States, municipalities and political subdivisions | Special revenue | South
Fixed maturities:
Amortized Cost	228,469	237,848
Gross Unrealized Appreciation	8,195	1,669
Gross Unrealized Depreciation	98	3,708
Fair Value	236,566	235,809
States, municipalities and political subdivisions | Special revenue | West
Fixed maturities:
Amortized Cost	142,661	143,829
Gross Unrealized Appreciation	4,664	1,294
Gross Unrealized Depreciation	8	2,203
Fair Value	147,317	142,920
Foreign bonds
Fixed maturities:
Amortized Cost	4,939	9,698
Gross Unrealized Appreciation	178	31
Gross Unrealized Depreciation	0	13
Fair Value	5,117	9,716
Public utilities
Fixed maturities:
Amortized Cost	62,749	56,808
Gross Unrealized Appreciation	2,031	274
Gross Unrealized Depreciation	62	1,023
Fair Value	64,718	56,059
Corporate bonds | Energy
Fixed maturities:
Amortized Cost	26,634	28,909
Gross Unrealized Appreciation	1,139	43
Gross Unrealized Depreciation	0	304
Fair Value	27,773	28,648
Corporate bonds | Industrials
Fixed maturities:
Amortized Cost	53,751	53,867
Gross Unrealized Appreciation	1,454	124
Gross Unrealized Depreciation	43	906
Fair Value	55,162	53,085
Corporate bonds | Consumer goods and services
Fixed maturities:
Amortized Cost	48,118	54,323
Gross Unrealized Appreciation	1,844	142
Gross Unrealized Depreciation	73	819
Fair Value	49,889	53,646
Corporate bonds | Health care
Fixed maturities:
Amortized Cost	13,982	16,721
Gross Unrealized Appreciation	585	42
Gross Unrealized Depreciation	0	105
Fair Value	14,567	16,658
Corporate bonds | Technology, media and telecommunications
Fixed maturities:
Amortized Cost	25,897	26,819
Gross Unrealized Appreciation	1,231	35
Gross Unrealized Depreciation	0	678
Fair Value	27,128	26,176
Corporate bonds | Financial services
Fixed maturities:
Amortized Cost	91,870	81,286
Gross Unrealized Appreciation	3,049	238
Gross Unrealized Depreciation	256	2,175
Fair Value	94,663	79,349
Mortgage-backed securities
Fixed maturities:
Amortized Cost	7,071	7,642
Gross Unrealized Appreciation	83	14
Gross Unrealized Depreciation	60	232
Fair Value	7,094	7,424
Collateralized mortgage obligations | Government National Mortgage Association (GNMA) Insured Loans
Fixed maturities:
Amortized Cost	76,524	78,055
Gross Unrealized Appreciation	2,022	380
Gross Unrealized Depreciation	80	1,734
Fair Value	78,466	76,701
Collateralized mortgage obligations | Federal Home Loan Mortgage Corporation (FHLMC) Insured Loans
Fixed maturities:
Amortized Cost	109,450	108,403
Gross Unrealized Appreciation	2,100	524
Gross Unrealized Depreciation	87	1,304
Fair Value	111,463	107,623
Collateralized mortgage obligations | Federal National Mortgage Association (FNMA) Insured Loans
Fixed maturities:
Amortized Cost	52,247	53,267
Gross Unrealized Appreciation	1,755	213
Gross Unrealized Depreciation	37	732
Fair Value	53,965	52,748
Asset-backed securities
Fixed maturities:
Amortized Cost	3,262	3,256
Gross Unrealized Appreciation	430	352
Gross Unrealized Depreciation	84	113
Fair Value	$ 3,608	$ 3,495