Fair Value of Financial Instruments (Financial Instruments Measured at Fair Value) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 1,703,319	$ 1,749,488
Trading securities	17,143	13,240
Equity securities	283,178	248,361
U.S. Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	29,072	27,418
U.S. government agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	140,050	214,682
States, municipalities and political subdivisions \| General obligations \| Midwest
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	89,370	95,212
States, municipalities and political subdivisions \| General obligations \| Northeast
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	32,324	37,655
States, municipalities and political subdivisions \| General obligations \| South
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	115,975	113,911
States, municipalities and political subdivisions \| General obligations \| West
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	109,893	107,841
States, municipalities and political subdivisions \| Special revenue \| Midwest
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	144,438	140,764
States, municipalities and political subdivisions \| Special revenue \| Northeast
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	64,701	61,948
States, municipalities and political subdivisions \| Special revenue \| South
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	236,566	235,809
States, municipalities and political subdivisions \| Special revenue \| West
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	147,317	142,920
Foreign bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	5,117	9,716
Public utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	64,718	56,059
Corporate bonds \| Energy
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	27,773	28,648
Corporate bonds \| Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	55,162	53,085
Corporate bonds \| Consumer goods and services
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	49,889	53,646
Corporate bonds \| Health care
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	14,567	16,658
Corporate bonds \| Technology, media and telecommunications
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	27,128	26,176
Corporate bonds \| Financial services
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	94,663	79,349
Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	7,094	7,424
Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	3,608	3,495
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,703,319	1,749,488
Trading securities	17,143	13,240
Equity securities	283,178	248,361
Short-term investments	175	175
Money market accounts	17,739	3,275
Corporate-owned life insurance	5,976	4,907
Total assets measured at fair value	2,027,530	2,019,446
Recurring \| Public utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	15,665	15,949
Recurring \| Energy
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	13,784	10,975
Recurring \| Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	59,931	53,536
Recurring \| Consumer goods and services
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	27,494	24,465
Recurring \| Health care
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	25,378	22,286
Recurring \| Technology, media and telecommunications
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	16,776	13,944
Recurring \| Financial services
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	118,779	101,555
Recurring \| U.S. Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	29,072	27,418
Trading securities	749
Recurring \| U.S. government agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	140,050	214,682
Recurring \| States, municipalities and political subdivisions \| General obligations \| Midwest
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	89,370	95,212
Recurring \| States, municipalities and political subdivisions \| General obligations \| Northeast
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	32,324	37,655
Recurring \| States, municipalities and political subdivisions \| General obligations \| South
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	115,975	113,911
Recurring \| States, municipalities and political subdivisions \| General obligations \| West
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	109,893	107,841
Recurring \| States, municipalities and political subdivisions \| Special revenue \| Midwest
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	144,438	140,764
Recurring \| States, municipalities and political subdivisions \| Special revenue \| Northeast
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	64,701	61,948
Recurring \| States, municipalities and political subdivisions \| Special revenue \| South
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	236,566	235,809
Recurring \| States, municipalities and political subdivisions \| Special revenue \| West
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	147,317	142,920
Recurring \| Foreign bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	5,117	9,716
Recurring \| Public utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	64,718	56,059
Recurring \| Corporate bonds \| Energy
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	27,773	28,648
Recurring \| Corporate bonds \| Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	55,162	53,085
Trading securities	398	397
Recurring \| Corporate bonds \| Consumer goods and services
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	49,889	53,646
Trading securities	1,905	1,599
Recurring \| Corporate bonds \| Health care
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	14,567	16,658
Trading securities	5,164	3,236
Recurring \| Corporate bonds \| Technology, media and telecommunications
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	27,128	26,176
Trading securities	3,065	3,028
Recurring \| Corporate bonds \| Financial services
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	94,663	79,349
Trading securities	2,006	2,231
Recurring \| Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	7,094	7,424
Recurring \| Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	3,608	3,495
Recurring \| Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	3,856	2,749
Recurring \| Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	5,371	5,651
Recurring \| Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Trading securities	3,856	2,749
Equity securities	282,583	247,766
Short-term investments	175	175
Money market accounts	17,739	3,275
Corporate-owned life insurance	0	0
Total assets measured at fair value	304,353	253,965
Recurring \| Level 1 \| Public utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	15,665	15,949
Recurring \| Level 1 \| Energy
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	13,784	10,975
Recurring \| Level 1 \| Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	59,931	53,536
Recurring \| Level 1 \| Consumer goods and services
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	27,494	24,465
Recurring \| Level 1 \| Health care
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	25,378	22,286
Recurring \| Level 1 \| Technology, media and telecommunications
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	16,776	13,944
Recurring \| Level 1 \| Financial services
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	118,779	101,555
Recurring \| Level 1 \| U.S. Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Trading securities	0
Recurring \| Level 1 \| U.S. government agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 1 \| States, municipalities and political subdivisions \| General obligations \| Midwest
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 1 \| States, municipalities and political subdivisions \| General obligations \| Northeast
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 1 \| States, municipalities and political subdivisions \| General obligations \| South
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 1 \| States, municipalities and political subdivisions \| General obligations \| West
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 1 \| States, municipalities and political subdivisions \| Special revenue \| Midwest
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 1 \| States, municipalities and political subdivisions \| Special revenue \| Northeast
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 1 \| States, municipalities and political subdivisions \| Special revenue \| South
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 1 \| States, municipalities and political subdivisions \| Special revenue \| West
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 1 \| Foreign bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 1 \| Public utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 1 \| Corporate bonds \| Energy
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 1 \| Corporate bonds \| Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Trading securities	0	0
Recurring \| Level 1 \| Corporate bonds \| Consumer goods and services
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Trading securities	0	0
Recurring \| Level 1 \| Corporate bonds \| Health care
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Trading securities	0	0
Recurring \| Level 1 \| Corporate bonds \| Technology, media and telecommunications
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Trading securities	0	0
Recurring \| Level 1 \| Corporate bonds \| Financial services
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Trading securities	0	0
Recurring \| Level 1 \| Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 1 \| Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 1 \| Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	3,856	2,749
Recurring \| Level 1 \| Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	4,776	5,056
Recurring \| Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,702,325	1,748,572
Trading securities	13,287	10,491
Equity securities	0	0
Short-term investments	0	0
Money market accounts	0	0
Corporate-owned life insurance	5,976	4,907
Total assets measured at fair value	1,721,588	1,763,970
Recurring \| Level 2 \| Public utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0	0
Recurring \| Level 2 \| Energy
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0	0
Recurring \| Level 2 \| Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0	0
Recurring \| Level 2 \| Consumer goods and services
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0	0
Recurring \| Level 2 \| Health care
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0	0
Recurring \| Level 2 \| Technology, media and telecommunications
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0	0
Recurring \| Level 2 \| Financial services
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0	0
Recurring \| Level 2 \| U.S. Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	29,072	27,418
Trading securities	749
Recurring \| Level 2 \| U.S. government agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	140,050	214,682
Recurring \| Level 2 \| States, municipalities and political subdivisions \| General obligations \| Midwest
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	89,370	95,212
Recurring \| Level 2 \| States, municipalities and political subdivisions \| General obligations \| Northeast
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	32,324	37,655
Recurring \| Level 2 \| States, municipalities and political subdivisions \| General obligations \| South
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	115,975	113,911
Recurring \| Level 2 \| States, municipalities and political subdivisions \| General obligations \| West
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	109,893	107,841
Recurring \| Level 2 \| States, municipalities and political subdivisions \| Special revenue \| Midwest
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	144,438	140,764
Recurring \| Level 2 \| States, municipalities and political subdivisions \| Special revenue \| Northeast
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	64,701	61,948
Recurring \| Level 2 \| States, municipalities and political subdivisions \| Special revenue \| South
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	236,566	235,809
Recurring \| Level 2 \| States, municipalities and political subdivisions \| Special revenue \| West
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	147,317	142,920
Recurring \| Level 2 \| Foreign bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	5,117	9,716
Recurring \| Level 2 \| Public utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	64,718	56,059
Recurring \| Level 2 \| Corporate bonds \| Energy
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	27,773	28,648
Recurring \| Level 2 \| Corporate bonds \| Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	55,162	53,085
Trading securities	398	397
Recurring \| Level 2 \| Corporate bonds \| Consumer goods and services
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	49,889	53,646
Trading securities	1,905	1,599
Recurring \| Level 2 \| Corporate bonds \| Health care
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	14,567	16,658
Trading securities	5,164	3,236
Recurring \| Level 2 \| Corporate bonds \| Technology, media and telecommunications
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	27,128	26,176
Trading securities	3,065	3,028
Recurring \| Level 2 \| Corporate bonds \| Financial services
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	94,413	79,099
Trading securities	2,006	2,231
Recurring \| Level 2 \| Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	7,094	7,424
Recurring \| Level 2 \| Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	2,864	2,829
Recurring \| Level 2 \| Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	0	0
Recurring \| Level 2 \| Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0	0
Recurring \| Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	994	916
Trading securities	0	0
Equity securities	595	595
Short-term investments	0	0
Money market accounts	0	0
Corporate-owned life insurance	0	0
Total assets measured at fair value	1,589	1,511
Recurring \| Level 3 \| Public utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0	0
Recurring \| Level 3 \| Energy
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0	0
Recurring \| Level 3 \| Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0	0
Recurring \| Level 3 \| Consumer goods and services
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0	0
Recurring \| Level 3 \| Health care
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0	0
Recurring \| Level 3 \| Technology, media and telecommunications
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0	0
Recurring \| Level 3 \| Financial services
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0	0
Recurring \| Level 3 \| U.S. Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Trading securities	0
Recurring \| Level 3 \| U.S. government agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 3 \| States, municipalities and political subdivisions \| General obligations \| Midwest
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 3 \| States, municipalities and political subdivisions \| General obligations \| Northeast
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 3 \| States, municipalities and political subdivisions \| General obligations \| South
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 3 \| States, municipalities and political subdivisions \| General obligations \| West
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 3 \| States, municipalities and political subdivisions \| Special revenue \| Midwest
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 3 \| States, municipalities and political subdivisions \| Special revenue \| Northeast
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 3 \| States, municipalities and political subdivisions \| Special revenue \| South
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 3 \| States, municipalities and political subdivisions \| Special revenue \| West
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 3 \| Foreign bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 3 \| Public utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 3 \| Corporate bonds \| Energy
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 3 \| Corporate bonds \| Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Trading securities	0	0
Recurring \| Level 3 \| Corporate bonds \| Consumer goods and services
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Trading securities	0	0
Recurring \| Level 3 \| Corporate bonds \| Health care
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Trading securities	0	0
Recurring \| Level 3 \| Corporate bonds \| Technology, media and telecommunications
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Trading securities	0	0
Recurring \| Level 3 \| Corporate bonds \| Financial services
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	250	250
Trading securities	0	0
Recurring \| Level 3 \| Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Recurring \| Level 3 \| Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	744	666
Recurring \| Level 3 \| Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	0	0
Recurring \| Level 3 \| Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	595	595
Government National Mortgage Association (GNMA) Insured Loans \| Collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	78,466	76,701
Government National Mortgage Association (GNMA) Insured Loans \| Recurring \| Collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	78,466	76,701
Government National Mortgage Association (GNMA) Insured Loans \| Recurring \| Level 1 \| Collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Government National Mortgage Association (GNMA) Insured Loans \| Recurring \| Level 2 \| Collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	78,466	76,701
Government National Mortgage Association (GNMA) Insured Loans \| Recurring \| Level 3 \| Collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Federal Home Loan Mortgage Corporation (FHLMC) Insured Loans \| Collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	111,463	107,623
Federal Home Loan Mortgage Corporation (FHLMC) Insured Loans \| Recurring \| Collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	111,463	107,623
Federal Home Loan Mortgage Corporation (FHLMC) Insured Loans \| Recurring \| Level 1 \| Collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Federal Home Loan Mortgage Corporation (FHLMC) Insured Loans \| Recurring \| Level 2 \| Collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	111,463	107,623
Federal Home Loan Mortgage Corporation (FHLMC) Insured Loans \| Recurring \| Level 3 \| Collateralized mortgage obligations

Fair Value of Financial Instruments (Financial Instruments Measured at Fair Value) (Details) - USD ($)
$ in Thousands

Jun. 30, 2019

Dec. 31, 2018

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Available-for-sale securities

$ 1,703,319

$ 1,749,488

Trading securities

17,143

13,240

Equity securities

283,178