Reserves for Losses and Loss Adjustment Expenses (Incurred and Paid Claims Development - Property) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) claim	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total unfavorable (favorable) net prior year development	$ 58,288	$ 60,900
Incurred claims and claim adjustment expenses related to current year	332,863	301,265
Total incurred	412,851	362,165
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	185,407	192,335
Paid claims and allocated claim adjustment expenses related to current year	113,312	127,610
Total paid	320,419	319,945
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	440,183	347,751	$ 305,531
Loss Adjustment Expenses Recognized In 2011 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years										$ 2,897
Property [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total incurred	224,636
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Total paid	197,634
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	27,002
Property [Member] | Loss Adjustment Expenses Recognized In 2011 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total unfavorable (favorable) net prior year development		12,549	12,551	$ 12,494	$ 12,616	$ 12,598	$ 12,406	$ 12,228	$ 12,289	11,768
Incurred claims and claim adjustment expenses related to current year	$ 12,549
Cumulative number of reported claims | claim	1,512
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 12,549	12,549	12,551	12,550	12,541	12,492	12,370	12,343	12,354	$ 10,317
Property [Member] | Loss Adjustment Expenses Recognized In 2012 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total unfavorable (favorable) net prior year development		17,963	17,974	18,005	17,768	17,743	18,119	17,541	18,518
Incurred claims and claim adjustment expenses related to current year	$ 17,963
Cumulative number of reported claims | claim	1,629
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 17,963	17,963	17,974	17,978	17,693	17,666	17,743	17,679	$ 15,773
Property [Member] | Loss Adjustment Expenses Recognized In 2013 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total unfavorable (favorable) net prior year development		22,935	22,936	22,914	22,578	22,264	22,363	21,644
Incurred claims and claim adjustment expenses related to current year	$ 22,935
Cumulative number of reported claims | claim	1,893
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 22,935	22,935	22,936	22,826	22,197	21,864	21,452	$ 17,785
Property [Member] | Loss Adjustment Expenses Recognized In 2014 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total unfavorable (favorable) net prior year development		21,876	21,852	21,793	21,862	21,950	22,551
Incurred claims and claim adjustment expenses related to current year	21,932
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ (81)
Cumulative number of reported claims | claim	2,037
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 22,013	21,955	21,911	21,849	21,778	21,749	$ 19,586
Property [Member] | Loss Adjustment Expenses Recognized in 2015 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total unfavorable (favorable) net prior year development		20,202	20,091	20,014	19,919	20,256
Incurred claims and claim adjustment expenses related to current year	20,107
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 142
Cumulative number of reported claims | claim	1,993
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 19,965	19,953	20,134	19,928	19,500	$ 17,513
Property [Member] | Loss Adjustment Expenses Recognized in 2016 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total unfavorable (favorable) net prior year development		22,789	22,632	22,838	20,734
Incurred claims and claim adjustment expenses related to current year	22,781
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 0
Cumulative number of reported claims | claim	2,031
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 22,781	22,789	22,613	22,500	$ 17,248
Property [Member] | Loss Adjustment Expenses Recognized in 2017 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total unfavorable (favorable) net prior year development		24,490	23,003	24,182
Incurred claims and claim adjustment expenses related to current year	24,287
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 1
Cumulative number of reported claims | claim	2,007
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 24,179	23,821	22,059	$ 18,703
Property [Member] | Loss Adjustment Expenses Recognized In 2018 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total unfavorable (favorable) net prior year development		18,694	22,822
Incurred claims and claim adjustment expenses related to current year	19,611
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 114
Cumulative number of reported claims | claim	1,064
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 18,138	16,914	$ 10,923
Property [Member] | Loss Adjustment Expenses Recognized In 2019 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total unfavorable (favorable) net prior year development		20,214
Incurred claims and claim adjustment expenses related to current year	20,984
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 181
Cumulative number of reported claims | claim	1,182
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 18,895	$ 11,344
Property [Member] | Loss Adjustment Expenses Recognized In 2020 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Incurred claims and claim adjustment expenses related to current year	41,487
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 12,769
Cumulative number of reported claims | claim	1,330
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to current year	$ 18,215