Investments (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Available-For-Sale Securities [Line Items]
Applicable federal income taxes	$ (19,098)	$ (14,319)
Net unrealized gains - net of tax	35,467	26,592
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Number of Securities, Total	259	289
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair value, total	123,485	106,933
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross unrealized loss, total	(2,937)	(4,538)
Major Categories of Investment Income [Line Items]
Investment Income	12,216	12,814	13,342
Investment expenses	(2,286)	(2,085)	(2,007)
Net investment income	9,930	10,729	11,335
Gain and Loss on Investment [Abstract]
Limited partnerships - net gain (loss)	7,052	(21,890)	8,206
Total net gains (losses)	9,011	(17,803)	16,485
Shareholders' equity, net of deferred federal income taxes and undistributed earnings from limited partnership	20,000
Adjustments for other-than-temporary impairment [Roll Forward]
Cumulative charges to income at beginning of year	8,178	7,604	9,235
Writedowns based on objective and subjective criteria	888	1,906	42
Recovery of prior write-downs upon sale or disposal	(1,293)	(1,332)	(1,673)
Net pre-tax realized gain (loss)	405	(574)	1,631
Cumulative charges to income at end of year	7,773	8,178	7,604
Addition (reduction) to earnings per share from net after-tax realized gain (loss) (in dollars per share)	$ 0.02	$ (0.03)	$ 0.07
Unrealized gain on investments previously written down at end of the year - see note below	8,158	6,782	9,535
Limited Partners' Capital Account [Line Items]
Number of partnerships investment	3
Market value of equity and fixed maturity securities portfolio managed by broker-dealers	1,869	19,300
Total commissions and net fees earned by broker dealers and affiliates	186	174	155
Summarized financial information of significant limited partnership investments [Abstract]
Total assets	983,024	905,294
Regulatory deposits with various insurance departments in United States and Canada, fair value	47,791	41,758
Time certificate of deposit included in short-term investments	4,201
Percentage of fixed maturities invested in investment grade fixed maturity (in hundredths)	90.00%
Total fixed maturity investments	35,300
Number of different investments in fixed maturity	17
Number of different third party insurance companies issuing fixed maturity investments with guarantees	3
Amount of largest exposure to a single investment	5,300
Percentage of fixed maturity investment to total invested assets (in hundredths)	6.30%
Number of investments in diversified portfolio including catastrophe bonds	40
Net unrealized loss position of diversified portfolio	408
Limited Partnership [Member]
Limited Partners' Capital Account [Line Items]
Commitment to make additional contributions to various limited partnerships	7,846
Total investment in three limited partnerships	24,000
Number of partnerships investment	3
Aggregate estimated value of limited partnership	39,745
Number of directors that are executive officers, directors, and owners of the organization managing the limited partnership	3
Ownership interest in limited partnership, minimum (in hundredths)	4.00%
Ownership interest in limited partnership, maximum (in hundredths)	14.00%
Investment gains (losses), net of fees	2,485	(18,673)	7,464
Management fees	650	793	820
Performance-based fees	0	0	687
Summarized financial information of significant limited partnership investments [Abstract]
Total partners' capital	39,745
Significant Limited Partnership [Member]
Limited Partners' Capital Account [Line Items]
Aggregate estimated value of limited partnership	559,745	579,568	895,207
Number of significant investments in public and private equity market in India	1
Significant investment in public and private equity markets in India, value	25,868	23,465
Estimated ownership interest in significant limited partnership investment (in hundredths)	4.00%
Earnings from significant limited partnership investment	2,404	(9,732)	3,521
Summarized financial information of significant limited partnership investments [Abstract]
Total assets	641,071	633,165	963,207
Total partners' capital	559,745	579,568	895,207
Net increase in partners' capital resulting from operations	60,734	(266,314)	98,279
Fixed Maturities [Member]
Major Categories of Investment Income [Line Items]
Investment Income	10,052	11,016	11,838
Equity Securities [Member]
Major Categories of Investment Income [Line Items]
Investment Income	2,121	1,738	1,433
Money Market Funds [Member]
Major Categories of Investment Income [Line Items]
Investment Income	38	36	39
Short-term and Other [Member]
Major Categories of Investment Income [Line Items]
Investment Income	5	24	32
U.S. Government Obligations [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	70,742	73,137
Cost or Amortized Cost	70,720	73,009
Gross Unrealized Gains	43	139
Gross Unrealized Losses	(21)	(11)
Net Unrealized Gains (losses)	22	128
Government Sponsored Entities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value		349
Cost or Amortized Cost		345
Gross Unrealized Gains		4
Gross Unrealized Losses		0
Net Unrealized Gains (losses)		4
Residential mortgage-backed securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	25,040	21,872
Cost or Amortized Cost	23,954	21,778
Gross Unrealized Gains	1,218	619
Gross Unrealized Losses	(132)	(525)
Net Unrealized Gains (losses)	1,086	94
Commercial Mortgage-backed Securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	11,828	11,300
Cost or Amortized Cost	11,006	11,388
Gross Unrealized Gains	849	116
Gross Unrealized Losses	(27)	(204)
Net Unrealized Gains (losses)	822	(88)
State and Municipal Obligations [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	194,865	190,035
Cost or Amortized Cost	194,258	188,991
Gross Unrealized Gains	757	1,275
Gross Unrealized Losses	(150)	(231)
Net Unrealized Gains (losses)	607	1,044
Corporate Securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	120,596	91,646
Cost or Amortized Cost	118,574	91,949
Gross Unrealized Gains	2,923	1,429
Gross Unrealized Losses	(901)	(1,732)
Net Unrealized Gains (losses)	2,022	(303)
Foreign Government Obligations [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	22,598	21,121
Cost or Amortized Cost	22,047	21,483
Gross Unrealized Gains	602	168
Gross Unrealized Losses	(51)	(530)
Net Unrealized Gains (losses)	551	(362)
Fixed Maturities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	445,669	409,460
Cost or Amortized Cost	440,559	408,943
Gross Unrealized Gains	6,392	3,750
Gross Unrealized Losses	(1,282)	(3,233)
Net Unrealized Gains (losses)	5,110	517
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Number of Securities 12 months or less	170	206
Number of Securities Greater than 12 months	58	44
Number of Securities, Total	228	250
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair value, 12 months or less	90,607	86,470
Fair value, Greater than 12 months	19,283	11,930
Fair value, total	109,890	98,400
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross unrealized loss, less than 12 months	(483)	(2,303)
Gross unrealized loss, 12 months or longer	(799)	(930)
Gross unrealized loss, total	(1,282)	(3,233)
Average unrealized loss for securities in loss position (in hundredths)	1.00%
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
One year or less	152,034
Excess of one year to five years	222,173
Excess of five years to ten years	21,492
Excess of ten years	3,137
Total maturities	398,836
Asset-backed securities	46,833
Available-for-sale Securities, Debt Securities, Total	445,669
Percentage of Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
One year or less (in hundredths)	34.10%
Excess of one year to five years (in hundredths)	49.90%
Excess of five years to ten years (in hundredths)	4.80%
Excess of ten years (in hundredths)	0.70%
Total maturities (in hundredths)	89.50%
Asset-backed securities (in hundredths)	10.50%
Available-for-sale Securities, Debt Securities, Total (in hundredths)	100.00%
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis [Abstract]
One year or less	151,687
Excess of one year to five years	220,010
Excess of five years to ten years	21,122
Excess of ten years	3,044
Total maturities	395,863
Asset-backed securities	44,696
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Total	440,559
Percentage of Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
One year or less (in hundredths)	34.40%
Excess of one year to five years (in hundredths)	49.90%
Excess of five years to ten years (in hundredths)	4.80%
Excess of ten years (in hundredths)	0.70%
Total maturities (in hundredths)	89.80%
Asset-backed securities (in hundredths)	10.20%
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Total (in hundredths)	100.00%
Gain and Loss on Investment [Abstract]
Gross gains	3,860	6,443	4,005
Gross losses	(3,961)	(6,805)	(1,215)
Net gains (losses)	(101)	(362)	2,790
Financial Institutions [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	12,394	9,428
Cost or Amortized Cost	5,925	4,955
Gross Unrealized Gains	6,542	4,778
Gross Unrealized Losses	(73)	(305)
Net Unrealized Gains (losses)	6,469	4,473
Industrial & Miscellaneous [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	95,188	78,657
Cost or Amortized Cost	52,202	42,736
Gross Unrealized Gains	44,568	36,921
Gross Unrealized Losses	(1,582)	(1,000)
Net Unrealized Gains (losses)	42,986	35,921
Equity Securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	107,582	88,085
Cost or Amortized Cost	58,127	47,691
Gross Unrealized Gains	51,110	41,699
Gross Unrealized Losses	(1,655)	(1,305)
Net Unrealized Gains (losses)	49,455	40,394
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Number of Securities 12 months or less	20	35
Number of Securities Greater than 12 months	11	4
Number of Securities, Total	31	39
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair value, 12 months or less	6,955	8,317
Fair value, Greater than 12 months	6,640	216
Fair value, total	13,595	8,533
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross unrealized loss, less than 12 months	(842)	(1,275)
Gross unrealized loss, 12 months or longer	(813)	(30)
Gross unrealized loss, total	(1,655)	(1,305)
Gain and Loss on Investment [Abstract]
Gross gains	3,191	7,409	7,447
Gross losses	(1,131)	(2,960)	(1,958)
Net gains (losses)	2,060	4,449	5,489
Total Available-for-Sale Securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	553,251	497,545
Cost or Amortized Cost	498,686	456,634
Gross Unrealized Gains	57,502	45,449
Gross Unrealized Losses	(2,937)	(4,538)
Net Unrealized Gains (losses)	$ 54,565	$ 40,911