Reserves for Unpaid Losses and Loss Adjustment Expenses (Incurred and Paid Claims Development - Standard Commercial Segment) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) claim	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2008 USD ($)	Dec. 31, 2007 USD ($)
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Incurred claims and claim adjustment expenses related to prior years	$ 7,608	$ (6,953)	$ (5,203)
Incurred claims and claim adjustment expenses related to current year	246,080	237,102	215,258
Total incurred	253,688	230,149	210,055
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	150,378	122,122	123,100
Paid claims and allocated claim adjustment expenses related to current year	93,067	83,132	76,231
Total paid	243,445	205,254	199,331
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	358,330	348,087	323,192	$ 312,468
Standard Commercial Segment [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total incurred	456,070
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Total paid	374,386
All outstanding liabilities before 2007, net of reinsurance	538
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	82,222
Standard Commercial Segment [Member] | Loss Adjustment Expenses Recognized In 2007 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Incurred claims and claim adjustment expenses related to prior years	36,419	37,321	36,798	37,894	$ 39,476	$ 41,814	$ 42,898	$ 42,632	$ 45,280	$ 48,423
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 576
Cumulative number of reported claims | claim	3,156
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 34,483	33,982	33,561	32,949	32,288	31,311	28,908	25,484	20,362	$ 13,883
Standard Commercial Segment [Member] | Loss Adjustment Expenses Recognized In 2008 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Incurred claims and claim adjustment expenses related to prior years	39,195	40,001	40,387	41,597	42,758	45,556	46,762	47,557	49,452
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 1,826
Cumulative number of reported claims | claim	3,246
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 36,859	36,276	35,360	34,762	34,056	32,523	29,058	25,624	$ 17,182
Standard Commercial Segment [Member] | Loss Adjustment Expenses Recognized In 2009 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Incurred claims and claim adjustment expenses related to prior years	43,107	43,851	44,159	45,970	46,778	46,772	45,674	44,719
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 2,102
Cumulative number of reported claims | claim	2,632
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 40,629	40,575	40,389	38,316	35,818	32,075	28,313	$ 15,242
Standard Commercial Segment [Member] | Loss Adjustment Expenses Recognized In 2010 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Incurred claims and claim adjustment expenses related to prior years	42,175	42,426	43,459	43,164	44,847	45,235	45,263
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 2,252
Cumulative number of reported claims | claim	2,903
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 39,706	39,115	37,166	33,428	30,957	28,342	$ 21,302
Standard Commercial Segment [Member] | Loss Adjustment Expenses Recognized In 2011 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Incurred claims and claim adjustment expenses related to prior years	47,423	47,266	49,268	55,156	56,489	60,236
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 3,387
Cumulative number of reported claims | claim	4,364
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 42,441	41,140	40,301	38,909	35,119	$ 24,899
Standard Commercial Segment [Member] | Loss Adjustment Expenses Recognized In 2012 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Incurred claims and claim adjustment expenses related to prior years	44,272	45,990	48,222	52,554	51,998
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 5,144
Cumulative number of reported claims | claim	3,212
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 38,526	37,191	34,789	32,203	$ 23,445
Standard Commercial Segment [Member] | Loss Adjustment Expenses Recognized In 2013 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Incurred claims and claim adjustment expenses related to prior years	53,174	56,703	57,528	55,482
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 6,379
Cumulative number of reported claims | claim	3,910
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 44,475	41,809	36,411	$ 23,123
Standard Commercial Segment [Member] | Loss Adjustment Expenses Recognized In 2014 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Incurred claims and claim adjustment expenses related to prior years	53,568	55,808	55,488
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 8,979
Cumulative number of reported claims | claim	3,531
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 41,514	37,122	$ 24,255
Standard Commercial Segment [Member] | Loss Adjustment Expenses Recognized in 2015 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Incurred claims and claim adjustment expenses related to prior years	49,857	49,571
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 11,946
Cumulative number of reported claims | claim	3,129
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 34,245	$ 19,085
Standard Commercial Segment [Member] | Loss Adjustment Expenses Recognized in 2016 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Incurred claims and claim adjustment expenses related to current year	46,880
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 16,885
Cumulative number of reported claims | claim	2,554
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to current year	$ 21,508