Reserves for Unpaid Losses and Loss Adjustment Expenses (Incurred and Paid Claims Development - Standard Commercial Segment) (Details) $ in Thousands	12 Months Ended
	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 ($)	Dec. 31, 2009 USD ($)
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Incurred claims and claim adjustment expenses related to prior years	$ 5,953	$ 40,105
Incurred claims and claim adjustment expenses related to current year	250,075	248,203
Total incurred	256,028	288,308
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	232,345	181,277
Paid claims and allocated claim adjustment expenses related to current year	90,640	92,873
Total paid	322,985	274,150
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	305,531	372,488	$ 358,330
Standard Commercial Segment [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total incurred	453,461
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Total paid	394,024
All outstanding liabilities before 2009, net of reinsurance	2,499
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	61,936
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	41,513	42,168	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	$ 139
Cumulative number of reported claims | claim	2,644
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 40,991	40,835	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	42,427	42,880	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	$ 146
Cumulative number of reported claims | claim	2,920
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 42,063	40,937	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	45,244	46,841	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	$ 478
Cumulative number of reported claims | claim	3,583
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 43,794	43,680	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	41,421	42,986	44,272	45,990	48,222	52,554	51,998
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 736
Cumulative number of reported claims | claim	3,228
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 40,646	40,408	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	49,039	52,076	53,174	56,703	57,528	55,482
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 596
Cumulative number of reported claims | claim	3,924
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 47,853	46,756	44,575	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	54,125	53,882	53,568	55,808	55,488
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 1,990
Cumulative number of reported claims | claim	3,571
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 48,395	45,779	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	47,277	50,053	49,857	49,571
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 1,873
Cumulative number of reported claims | claim	3,181
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 43,287	38,302	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 prior years	46,348	48,182	46,880
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 1,900
Cumulative number of reported claims | claim	2,822
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 38,778	32,006	$ 21,508
Standard Commercial Segment [Member] | Loss Adjustment Expenses Recognized in 2017 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Incurred claims and claim adjustment expenses related to prior years	43,169	41,393
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 8,000
Cumulative number of reported claims | claim	2,556
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 28,984	$ 16,755
Standard Commercial Segment [Member] | Loss Adjustment Expenses Recognized In 2018 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Incurred claims and claim adjustment expenses related to current year	42,898
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 16,384
Cumulative number of reported claims | claim	2,165
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to current year	$ 19,233