Fair Value of Financial Instruments (Financial Instruments Measured at Fair Value) (Details) $ in Thousands	3 Months Ended
Mar. 31, 2016 USD ($) security	Dec. 31, 2015 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	$ 3,092,982	$ 3,061,208
Trading Securities	$ 17,446	16,975
Number of securities transferred between Level 1 and 2 \| security	0
Fixed Maturities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	$ 2,855,166	2,824,961
U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	24,083	21,649
U.S. Government Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	179,816	233,030
States, Municipalities and Political Subdivisions [Member] \| General Obligations [Member] \| Midwest [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	166,136	165,456
States, Municipalities and Political Subdivisions [Member] \| General Obligations [Member] \| Northeast [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	63,927	58,445
States, Municipalities and Political Subdivisions [Member] \| General Obligations [Member] \| South [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	123,419	128,789
States, Municipalities and Political Subdivisions [Member] \| General Obligations [Member] \| West [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	110,444	106,814
States, Municipalities and Political Subdivisions [Member] \| Special Revenue [Member] \| Midwest [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	163,088	157,706
States, Municipalities and Political Subdivisions [Member] \| Special Revenue [Member] \| Northeast [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	30,342	24,599
States, Municipalities and Political Subdivisions [Member] \| Special Revenue [Member] \| South [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	166,270	148,437
States, Municipalities and Political Subdivisions [Member] \| Special Revenue [Member] \| West [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	84,656	82,041
Foreign Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	80,745	82,528
Public Utilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	221,920	215,683
Corporate Bonds [Member] \| Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	114,682	113,119
Corporate Bonds [Member] \| Industrials [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	244,122	224,255
Corporate Bonds [Member] \| Consumer Goods and Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	183,784	174,597
Corporate Bonds [Member] \| Health Care [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	91,526	93,509
Corporate Bonds [Member] \| Technology, Media and Telecommunications [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	144,537	142,400
Corporate Bonds [Member] \| Financial Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	261,022	263,485
Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	15,799	16,738
Government National Mortgage Association [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	127,089	119,626
Federal Home Loan Mortgage Corporation [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	139,511	138,909
Federal National Mortgage Association [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	113,433	107,480
Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	4,815	5,666
Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	237,816	236,247
Common Stocks [Member] \| Public Utilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	21,943	19,060
Common Stocks [Member] \| Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	12,765	11,211
Common Stocks [Member] \| Industrials [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	45,742	44,810
Common Stocks [Member] \| Consumer Goods and Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	24,274	23,315
Common Stocks [Member] \| Health Care [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	26,871	28,217
Common Stocks [Member] \| Technology, Media and Telecommunications [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	14,424	13,364
Common Stocks [Member] \| Financial Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	91,328	95,694
Nonredeemable Preferred Stocks [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	469	576
Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	3,092,982	3,061,208
Trading Securities	17,446	16,975
Short-Term Investments	175	175
Money Market Accounts	63,567	20,805
Corporate-Owned Life Insurance	2,160	1,716
Total Assets Measured at Fair Value	3,176,330	3,100,879
Recurring [Member] \| Fixed Maturities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	2,855,166	2,824,961
Recurring [Member] \| U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	24,083	21,649
Recurring [Member] \| U.S. Government Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	179,816	233,030
Recurring [Member] \| States, Municipalities and Political Subdivisions [Member] \| General Obligations [Member] \| Midwest [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	166,136	165,456
Recurring [Member] \| States, Municipalities and Political Subdivisions [Member] \| General Obligations [Member] \| Northeast [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	63,927	58,445
Recurring [Member] \| States, Municipalities and Political Subdivisions [Member] \| General Obligations [Member] \| South [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	123,419	128,789
Recurring [Member] \| States, Municipalities and Political Subdivisions [Member] \| General Obligations [Member] \| West [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	110,444	106,814
Recurring [Member] \| States, Municipalities and Political Subdivisions [Member] \| Special Revenue [Member] \| Midwest [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	163,088	157,706
Recurring [Member] \| States, Municipalities and Political Subdivisions [Member] \| Special Revenue [Member] \| Northeast [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	30,342	24,599
Recurring [Member] \| States, Municipalities and Political Subdivisions [Member] \| Special Revenue [Member] \| South [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	166,270	148,437
Recurring [Member] \| States, Municipalities and Political Subdivisions [Member] \| Special Revenue [Member] \| West [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	84,656	82,041
Recurring [Member] \| Foreign Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	80,745	82,528
Recurring [Member] \| Public Utilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	221,920	215,683
Recurring [Member] \| Corporate Bonds [Member] \| Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	114,682	113,119
Recurring [Member] \| Corporate Bonds [Member] \| Industrials [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	244,122	224,255
Trading Securities	3,644	3,558
Recurring [Member] \| Corporate Bonds [Member] \| Consumer Goods and Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	183,784	174,597
Trading Securities	272	118
Recurring [Member] \| Corporate Bonds [Member] \| Health Care [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	91,526	93,509
Trading Securities	1,930	2,032
Recurring [Member] \| Corporate Bonds [Member] \| Technology, Media and Telecommunications [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	144,537	142,400
Trading Securities	338	335
Recurring [Member] \| Corporate Bonds [Member] \| Financial Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	261,022	263,485
Trading Securities	4,069	4,094
Recurring [Member] \| Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	15,799	16,738
Recurring [Member] \| Government National Mortgage Association [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	127,089	119,626
Recurring [Member] \| Federal Home Loan Mortgage Corporation [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	139,511	138,909
Recurring [Member] \| Federal National Mortgage Association [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	113,433	107,480
Recurring [Member] \| Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	4,815	5,666
Trading Securities	0
Recurring [Member] \| Redeemable Preferred Stocks [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	2,747	2,485
Recurring [Member] \| Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	237,816	236,247
Recurring [Member] \| Equity Securities [Member] \| Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	293	267
Recurring [Member] \| Equity Securities [Member] \| Industrials [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	1,027	986
Recurring [Member] \| Equity Securities [Member] \| Consumer Goods and Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	899	942
Recurring [Member] \| Equity Securities [Member] \| Health Care [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	304	304
Recurring [Member] \| Equity Securities [Member] \| Financial Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	235	229
Recurring [Member] \| Common Stocks [Member] \| Public Utilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	21,943	19,060
Recurring [Member] \| Common Stocks [Member] \| Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	12,765	11,211
Recurring [Member] \| Common Stocks [Member] \| Industrials [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	45,742	44,810
Recurring [Member] \| Common Stocks [Member] \| Consumer Goods and Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	24,274	23,315
Recurring [Member] \| Common Stocks [Member] \| Health Care [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	26,871	28,217
Recurring [Member] \| Common Stocks [Member] \| Technology, Media and Telecommunications [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	14,424	13,364
Recurring [Member] \| Common Stocks [Member] \| Financial Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	91,328	95,694
Recurring [Member] \| Nonredeemable Preferred Stocks [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	469	576
Trading Securities	1,688	1,625
Recurring [Member] \| Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	233,824	232,141
Trading Securities	7,193	6,838
Short-Term Investments	175	175
Money Market Accounts	63,567	20,805
Corporate-Owned Life Insurance	0	0
Total Assets Measured at Fair Value	304,759	259,959
Recurring [Member] \| Level 1 [Member] \| Fixed Maturities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 1 [Member] \| U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 1 [Member] \| U.S. Government Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 1 [Member] \| States, Municipalities and Political Subdivisions [Member] \| General Obligations [Member] \| Midwest [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 1 [Member] \| States, Municipalities and Political Subdivisions [Member] \| General Obligations [Member] \| Northeast [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 1 [Member] \| States, Municipalities and Political Subdivisions [Member] \| General Obligations [Member] \| South [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 1 [Member] \| States, Municipalities and Political Subdivisions [Member] \| General Obligations [Member] \| West [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 1 [Member] \| States, Municipalities and Political Subdivisions [Member] \| Special Revenue [Member] \| Midwest [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 1 [Member] \| States, Municipalities and Political Subdivisions [Member] \| Special Revenue [Member] \| Northeast [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 1 [Member] \| States, Municipalities and Political Subdivisions [Member] \| Special Revenue [Member] \| South [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 1 [Member] \| States, Municipalities and Political Subdivisions [Member] \| Special Revenue [Member] \| West [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 1 [Member] \| Foreign Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 1 [Member] \| Public Utilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 1 [Member] \| Corporate Bonds [Member] \| Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 1 [Member] \| Corporate Bonds [Member] \| Industrials [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Trading Securities	0	0
Recurring [Member] \| Level 1 [Member] \| Corporate Bonds [Member] \| Consumer Goods and Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Trading Securities	0	0
Recurring [Member] \| Level 1 [Member] \| Corporate Bonds [Member] \| Health Care [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Trading Securities	0	0
Recurring [Member] \| Level 1 [Member] \| Corporate Bonds [Member] \| Technology, Media and Telecommunications [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Trading Securities	0	0
Recurring [Member] \| Level 1 [Member] \| Corporate Bonds [Member] \| Financial Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Trading Securities	0	0
Recurring [Member] \| Level 1 [Member] \| Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 1 [Member] \| Government National Mortgage Association [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 1 [Member] \| Federal Home Loan Mortgage Corporation [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 1 [Member] \| Federal National Mortgage Association [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 1 [Member] \| Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Trading Securities	0
Recurring [Member] \| Level 1 [Member] \| Redeemable Preferred Stocks [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	2,747	2,485
Recurring [Member] \| Level 1 [Member] \| Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	233,824	232,141
Recurring [Member] \| Level 1 [Member] \| Equity Securities [Member] \| Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	293	267
Recurring [Member] \| Level 1 [Member] \| Equity Securities [Member] \| Industrials [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	1,027	986
Recurring [Member] \| Level 1 [Member] \| Equity Securities [Member] \| Consumer Goods and Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	899	942
Recurring [Member] \| Level 1 [Member] \| Equity Securities [Member] \| Health Care [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	304	304
Recurring [Member] \| Level 1 [Member] \| Equity Securities [Member] \| Financial Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	235	229
Recurring [Member] \| Level 1 [Member] \| Common Stocks [Member] \| Public Utilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	21,943	19,060
Recurring [Member] \| Level 1 [Member] \| Common Stocks [Member] \| Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	12,765	11,211
Recurring [Member] \| Level 1 [Member] \| Common Stocks [Member] \| Industrials [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	45,742	44,810
Recurring [Member] \| Level 1 [Member] \| Common Stocks [Member] \| Consumer Goods and Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	24,274	23,315
Recurring [Member] \| Level 1 [Member] \| Common Stocks [Member] \| Health Care [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	26,871	28,217
Recurring [Member] \| Level 1 [Member] \| Common Stocks [Member] \| Technology, Media and Telecommunications [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	14,424	13,364
Recurring [Member] \| Level 1 [Member] \| Common Stocks [Member] \| Financial Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	87,336	91,588
Recurring [Member] \| Level 1 [Member] \| Nonredeemable Preferred Stocks [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	469	576
Trading Securities	1,688	1,625
Recurring [Member] \| Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	2,843,181	2,812,815
Trading Securities	10,253	10,137
Short-Term Investments	0	0
Money Market Accounts	0	0
Corporate-Owned Life Insurance	2,160	1,716
Total Assets Measured at Fair Value	2,855,594	2,824,668
Recurring [Member] \| Level 2 [Member] \| Fixed Maturities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	2,843,181	2,812,687
Recurring [Member] \| Level 2 [Member] \| U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	24,083	21,649
Recurring [Member] \| Level 2 [Member] \| U.S. Government Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	179,816	233,030
Recurring [Member] \| Level 2 [Member] \| States, Municipalities and Political Subdivisions [Member] \| General Obligations [Member] \| Midwest [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	166,136	165,456
Recurring [Member] \| Level 2 [Member] \| States, Municipalities and Political Subdivisions [Member] \| General Obligations [Member] \| Northeast [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	63,927	58,445
Recurring [Member] \| Level 2 [Member] \| States, Municipalities and Political Subdivisions [Member] \| General Obligations [Member] \| South [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	123,419	128,789
Recurring [Member] \| Level 2 [Member] \| States, Municipalities and Political Subdivisions [Member] \| General Obligations [Member] \| West [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	110,444	106,814
Recurring [Member] \| Level 2 [Member] \| States, Municipalities and Political Subdivisions [Member] \| Special Revenue [Member] \| Midwest [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	162,744	157,363
Recurring [Member] \| Level 2 [Member] \| States, Municipalities and Political Subdivisions [Member] \| Special Revenue [Member] \| Northeast [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	30,342	24,599
Recurring [Member] \| Level 2 [Member] \| States, Municipalities and Political Subdivisions [Member] \| Special Revenue [Member] \| South [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	166,270	148,437
Recurring [Member] \| Level 2 [Member] \| States, Municipalities and Political Subdivisions [Member] \| Special Revenue [Member] \| West [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	84,656	82,041
Recurring [Member] \| Level 2 [Member] \| Foreign Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	80,745	82,528
Recurring [Member] \| Level 2 [Member] \| Public Utilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	221,920	215,683
Recurring [Member] \| Level 2 [Member] \| Corporate Bonds [Member] \| Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	114,682	113,119
Recurring [Member] \| Level 2 [Member] \| Corporate Bonds [Member] \| Industrials [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	244,122	224,255
Trading Securities	3,644	3,558
Recurring [Member] \| Level 2 [Member] \| Corporate Bonds [Member] \| Consumer Goods and Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	182,570	173,364
Trading Securities	272	118
Recurring [Member] \| Level 2 [Member] \| Corporate Bonds [Member] \| Health Care [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	91,526	93,509
Trading Securities	1,930	2,032
Recurring [Member] \| Level 2 [Member] \| Corporate Bonds [Member] \| Technology, Media and Telecommunications [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	144,537	142,400
Trading Securities	338	335
Recurring [Member] \| Level 2 [Member] \| Corporate Bonds [Member] \| Financial Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	251,520	253,823
Trading Securities	4,069	4,094
Recurring [Member] \| Level 2 [Member] \| Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	15,799	16,738
Recurring [Member] \| Level 2 [Member] \| Government National Mortgage Association [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	127,089	119,626
Recurring [Member] \| Level 2 [Member] \| Federal Home Loan Mortgage Corporation [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	139,511	138,909
Recurring [Member] \| Level 2 [Member] \| Federal National Mortgage Association [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	113,433	107,480
Recurring [Member] \| Level 2 [Member] \| Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	3,890	4,630
Trading Securities	0
Recurring [Member] \| Level 2 [Member] \| Redeemable Preferred Stocks [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	0	0
Recurring [Member] \| Level 2 [Member] \| Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	128
Recurring [Member] \| Level 2 [Member] \| Equity Securities [Member] \| Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	0	0
Recurring [Member] \| Level 2 [Member] \| Equity Securities [Member] \| Industrials [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	0	0
Recurring [Member] \| Level 2 [Member] \| Equity Securities [Member] \| Consumer Goods and Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	0	0
Recurring [Member] \| Level 2 [Member] \| Equity Securities [Member] \| Health Care [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	0	0
Recurring [Member] \| Level 2 [Member] \| Equity Securities [Member] \| Financial Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	0	0
Recurring [Member] \| Level 2 [Member] \| Common Stocks [Member] \| Public Utilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 2 [Member] \| Common Stocks [Member] \| Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 2 [Member] \| Common Stocks [Member] \| Industrials [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 2 [Member] \| Common Stocks [Member] \| Consumer Goods and Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 2 [Member] \| Common Stocks [Member] \| Health Care [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 2 [Member] \| Common Stocks [Member] \| Technology, Media and Telecommunications [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Recurring [Member] \| Level 2 [Member] \| Common Stocks [Member] \| Financial Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	128
Recurring [Member] \| Level 2 [Member] \| Nonredeemable Preferred Stocks [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
Trading Securities	0	0

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

3 Months Ended

Mar. 31, 2016

USD ($)

security

Dec. 31, 2015

USD ($)

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

Available-for-Sale Securities

$ 3,092,982

$ 3,061,208

Trading Securities