Unpaid Losses and Settlement Expenses (Summary of Cumulative Paid Losses and Settlement Expenses) (Details) claim in Thousands, $ in Thousands	Dec. 31, 2018 USD ($) claim	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	$ 222,148
Cumulative paid loss and settlement expenses, net of reinsurance	177,579
Unpaid loss and settlement expense, net of reinsurance	44,711
Property Line [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	79,415
Cumulative paid loss and settlement expenses, net of reinsurance	76,222
Unpaid loss and settlement expense, net of reinsurance	3,190
Workers Compensation and Liability Lines [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	142,733
Cumulative paid loss and settlement expenses, net of reinsurance	101,357
Unpaid loss and settlement expense, net of reinsurance	41,521
2009 [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	16,296	$ 16,290	$ 16,265	$ 16,176	$ 16,507	$ 16,681	$ 16,213	$ 15,438	$ 14,944	$ 16,505
Total IBNR plus expected development on reported claims	$ 16
Cumulative number of reported claims | claim	1,738
Cumulative paid loss and settlement expenses, net of reinsurance	$ 16,259	16,201	15,977	15,770	15,429	14,561	12,426	10,257	6,944	4,193
2009 [Member] | Property Line [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	4,339	4,339	4,370	4,352	4,409	4,562	4,406	3,889	4,099	4,560
Total IBNR plus expected development on reported claims	$ 1
Cumulative number of reported claims | claim	479
Cumulative paid loss and settlement expenses, net of reinsurance	$ 4,339	4,339	4,338	4,338	4,349	4,280	4,137	4,082	3,930	2,991
2009 [Member] | Workers Compensation and Liability Lines [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	11,957	11,951	11,895	11,824	12,098	12,119	11,807	11,549	10,845	11,945
Total IBNR plus expected development on reported claims	$ 15
Cumulative number of reported claims | claim	1,259
Cumulative paid loss and settlement expenses, net of reinsurance	$ 11,920	11,862	11,639	11,432	11,080	10,281	8,289	6,175	3,014	$ 1,202
2010 [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	16,331	16,330	16,313	16,480	16,819	16,363	15,514	16,144	16,119
Total IBNR plus expected development on reported claims	$ 33
Cumulative number of reported claims | claim	1,578
Cumulative paid loss and settlement expenses, net of reinsurance	$ 16,219	16,068	15,940	15,551	14,813	13,202	10,584	7,979	4,414
2010 [Member] | Property Line [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	4,862	4,899	4,891	5,006	5,118	4,992	4,831	5,105	5,644
Total IBNR plus expected development on reported claims	$ (12)
Cumulative number of reported claims | claim	485
Cumulative paid loss and settlement expenses, net of reinsurance	$ 4,874	4,874	4,873	4,818	4,791	4,740	4,719	4,584	3,166
2010 [Member] | Workers Compensation and Liability Lines [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	11,469	11,431	11,422	11,474	11,701	11,371	10,683	11,039	10,475
Total IBNR plus expected development on reported claims	$ 45
Cumulative number of reported claims | claim	1,093
Cumulative paid loss and settlement expenses, net of reinsurance	$ 11,345	11,194	11,067	10,733	10,022	8,462	5,865	3,395	$ 1,248
2011 [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	18,355	18,450	18,672	18,831	18,791	18,515	18,834	19,802
Total IBNR plus expected development on reported claims	$ 16
Cumulative number of reported claims | claim	2,011
Cumulative paid loss and settlement expenses, net of reinsurance	$ 18,250	18,107	17,560	16,678	14,592	12,300	10,112	6,996
2011 [Member] | Property Line [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	6,632	6,631	6,645	6,733	6,752	6,621	6,708	7,427
Total IBNR plus expected development on reported claims	$ 8
Cumulative number of reported claims | claim	655
Cumulative paid loss and settlement expenses, net of reinsurance	$ 6,623	6,623	6,589	6,556	6,520	6,459	6,351	5,327
2011 [Member] | Workers Compensation and Liability Lines [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	11,723	11,819	12,027	12,098	12,039	11,894	12,126	12,375
Total IBNR plus expected development on reported claims	$ 8
Cumulative number of reported claims | claim	1,356
Cumulative paid loss and settlement expenses, net of reinsurance	$ 11,627	11,484	10,971	10,122	8,072	5,841	3,761	$ 1,669
2012 [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	19,087	19,256	19,174	18,184	17,813	17,712	19,265
Total IBNR plus expected development on reported claims	$ 76
Cumulative number of reported claims | claim	1,832
Cumulative paid loss and settlement expenses, net of reinsurance	$ 18,625	18,225	17,239	14,689	11,958	9,422	6,129
2012 [Member] | Property Line [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	6,455	6,411	6,482	6,546	6,406	6,374	6,143
Total IBNR plus expected development on reported claims	$ 1
Cumulative number of reported claims | claim	507
Cumulative paid loss and settlement expenses, net of reinsurance	$ 6,469	6,472	6,326	6,362	6,369	6,401	4,949
2012 [Member] | Workers Compensation and Liability Lines [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	12,632	12,845	12,692	11,638	11,407	11,338	13,122
Total IBNR plus expected development on reported claims	$ 75
Cumulative number of reported claims | claim	1,325
Cumulative paid loss and settlement expenses, net of reinsurance	$ 12,156	11,753	10,913	8,327	5,589	3,021	$ 1,180
2013 [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	22,140	22,167	21,375	21,459	21,861	21,850
Total IBNR plus expected development on reported claims	$ 257
Cumulative number of reported claims | claim	1,796
Cumulative paid loss and settlement expenses, net of reinsurance	$ 21,250	20,446	18,661	15,834	12,235	8,435
2013 [Member] | Property Line [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	8,282	8,471	8,415	8,290	8,302	9,266
Total IBNR plus expected development on reported claims	$ (5)
Cumulative number of reported claims | claim	482
Cumulative paid loss and settlement expenses, net of reinsurance	$ 8,272	8,265	8,238	8,200	8,079	6,856
2013 [Member] | Workers Compensation and Liability Lines [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	13,858	13,696	12,960	13,169	13,559	12,584
Total IBNR plus expected development on reported claims	$ 262
Cumulative number of reported claims | claim	1,314
Cumulative paid loss and settlement expenses, net of reinsurance	$ 12,978	12,181	10,423	7,634	4,156	$ 1,579
2014 [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	24,698	24,601	23,139	22,330	22,250
Total IBNR plus expected development on reported claims	$ 624
Cumulative number of reported claims | claim	1,976
Cumulative paid loss and settlement expenses, net of reinsurance	$ 23,027	21,398	17,261	11,718	7,782
2014 [Member] | Property Line [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	7,817	7,883	7,798	7,586	8,865
Total IBNR plus expected development on reported claims	$ 33
Cumulative number of reported claims | claim	561
Cumulative paid loss and settlement expenses, net of reinsurance	$ 7,795	7,796	7,746	7,631	6,243
2014 [Member] | Workers Compensation and Liability Lines [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	16,881	16,718	15,341	14,744	13,385
Total IBNR plus expected development on reported claims	$ 591
Cumulative number of reported claims | claim	1,415
Cumulative paid loss and settlement expenses, net of reinsurance	$ 15,232	13,602	9,515	4,087	$ 1,539
2015 [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	21,496	21,157	21,370	24,289
Total IBNR plus expected development on reported claims	$ 1,092
Cumulative number of reported claims | claim	1,672
Cumulative paid loss and settlement expenses, net of reinsurance	$ 18,172	14,874	11,359	6,462
2015 [Member] | Property Line [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	7,634	7,717	7,494	7,693
Total IBNR plus expected development on reported claims	$ (17)
Cumulative number of reported claims | claim	427
Cumulative paid loss and settlement expenses, net of reinsurance	$ 7,645	7,474	7,040	5,057
2015 [Member] | Workers Compensation and Liability Lines [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	13,862	13,440	13,876	16,596
Total IBNR plus expected development on reported claims	$ 1,109
Cumulative number of reported claims | claim	1,245
Cumulative paid loss and settlement expenses, net of reinsurance	$ 10,527	7,400	4,319	$ 1,405
2016 [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	24,612	22,824	25,618
Total IBNR plus expected development on reported claims	$ 3,274
Cumulative number of reported claims | claim	1,623
Cumulative paid loss and settlement expenses, net of reinsurance	$ 16,426	13,109	7,647
2016 [Member] | Property Line [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	8,372	7,981	8,941
Total IBNR plus expected development on reported claims	$ 14
Cumulative number of reported claims | claim	447
Cumulative paid loss and settlement expenses, net of reinsurance	$ 8,236	7,624	6,157
2016 [Member] | Workers Compensation and Liability Lines [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	16,240	14,843	16,677
Total IBNR plus expected development on reported claims	$ 3,260
Cumulative number of reported claims | claim	1,176
Cumulative paid loss and settlement expenses, net of reinsurance	$ 8,190	5,485	$ 1,490
2017 [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	29,371	29,801
Total IBNR plus expected development on reported claims	$ 5,337
Cumulative number of reported claims | claim	1,738
Cumulative paid loss and settlement expenses, net of reinsurance	$ 18,901	11,578
2017 [Member] | Property Line [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	13,568	13,993
Total IBNR plus expected development on reported claims	$ (250)
Cumulative number of reported claims | claim	554
Cumulative paid loss and settlement expenses, net of reinsurance	$ 13,482	10,055
2017 [Member] | Workers Compensation and Liability Lines [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	15,803	15,808
Total IBNR plus expected development on reported claims	$ 5,587
Cumulative number of reported claims | claim	1,184
Cumulative paid loss and settlement expenses, net of reinsurance	$ 5,419	$ 1,523
2018 [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	29,762
Total IBNR plus expected development on reported claims	$ 10,476
Cumulative number of reported claims | claim	1,632
Cumulative paid loss and settlement expenses, net of reinsurance	$ 10,450
2018 [Member] | Property Line [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	11,454
Total IBNR plus expected development on reported claims	$ 323
Cumulative number of reported claims | claim	567
Cumulative paid loss and settlement expenses, net of reinsurance	$ 8,487
2018 [Member] | Workers Compensation and Liability Lines [Member]
Claims Development [Line Items]
Incurred loss and settlement expenses, net of reinsurance	18,308
Total IBNR plus expected development on reported claims	$ 10,153
Cumulative number of reported claims | claim	1,065
Cumulative paid loss and settlement expenses, net of reinsurance	$ 1,963
Years 2009 Through 2018 [Member]
Claims Development [Line Items]
Unpaid losses and settlement expense	44,569
Years 2009 Through 2018 [Member] | Property Line [Member]
Claims Development [Line Items]
Unpaid losses and settlement expense	3,193
Years 2009 Through 2018 [Member] | Workers Compensation and Liability Lines [Member]
Claims Development [Line Items]
Unpaid losses and settlement expense	41,376
Prior To 2009 [Member]
Claims Development [Line Items]
Unpaid losses and settlement expense	142
Prior To 2009 [Member] | Property Line [Member]
Claims Development [Line Items]
Unpaid losses and settlement expense	(3)
Prior To 2009 [Member] | Workers Compensation and Liability Lines [Member]
Claims Development [Line Items]
Unpaid losses and settlement expense	$ 145