Reserves for Losses and Loss Adjustment Expenses (Incurred and Paid Claims Development - Casualty) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($) claim	Dec. 31, 2020 USD ($)	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 ($)	Dec. 31, 2012 USD ($)
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total unfavorable (favorable) net prior year development	$ 6,040	$ 58,288
Incurred claims and claim adjustment expenses related to current year	269,204	326,919
Total incurred	275,244	406,907
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	177,571	185,407
Paid claims and allocated claim adjustment expenses related to current year	101,475	113,312
Total paid	279,046	320,419
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	428,766	432,568	$ 346,080
Loss Adjustment Expenses Recognized In 2012 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years										$ 1,181
E&S Casualty business unit [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total incurred	281,868
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Total paid	179,778
All outstanding liabilities before 2012, net of reinsurance	1,910
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	104,001
E&S Casualty business unit [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		13,400	12,944	$ 11,852	$ 12,390	$ 13,330	$ 12,230	$ 13,098	$ 11,301	13,020
Incurred claims and claim adjustment expenses related to current year	13,145
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ (454)
Cumulative number of reported claims | claim	752
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 13,038	12,725	12,572	11,357	10,938	10,255	8,037	6,096	2,666	$ 1,337
E&S Casualty business unit [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		13,274	13,330	12,205	12,874	12,792	12,384	12,002	13,379
Incurred claims and claim adjustment expenses related to current year	13,370
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ (502)
Cumulative number of reported claims | claim	810
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 12,972	12,478	12,255	11,866	11,134	9,212	5,461	3,190	$ 1,331
E&S Casualty business unit [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		13,140	13,167	11,676	11,663	12,034	14,007	15,590
Incurred claims and claim adjustment expenses related to current year	12,989
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ (524)
Cumulative number of reported claims | claim	950
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 13,189	13,003	12,365	11,327	8,075	5,499	4,196	$ 1,829
E&S Casualty business unit [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		16,931	15,945	15,266	15,046	16,746	17,362
Incurred claims and claim adjustment expenses related to current year	18,542
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 157
Cumulative number of reported claims | claim	1,033
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 16,573	15,729	16,158	13,553	8,258	4,133	$ 1,420
E&S Casualty business unit [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		17,508	18,625	16,927	16,513	16,039
Incurred claims and claim adjustment expenses related to current year	16,819
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ (1,083)
Cumulative number of reported claims | claim	1,061
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 17,848	17,111	16,442	11,269	5,672	$ 1,753
E&S Casualty business unit [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		18,023	20,360	15,751	17,845
Incurred claims and claim adjustment expenses related to current year	21,362
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 1,113
Cumulative number of reported claims | claim	1,656
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 19,633	16,264	11,268	5,884	$ 2,900
E&S Casualty business unit [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		23,856	24,590	23,056
Incurred claims and claim adjustment expenses related to current year	23,055
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ (5,305)
Cumulative number of reported claims | claim	2,251
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 22,898	15,363	8,027	$ 2,708
E&S Casualty business unit [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		43,426	34,610
Incurred claims and claim adjustment expenses related to current year	47,496
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 3,220
Cumulative number of reported claims | claim	2,938
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 32,705	17,177	$ 2,526
E&S Casualty business unit [Member] | Loss Adjustment Expenses Recognized In 2020 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total unfavorable (favorable) net prior year development		62,464
Incurred claims and claim adjustment expenses related to current year	60,706
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 16,107
Cumulative number of reported claims | claim	7,503
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 24,029	$ 6,176
E&S Casualty business unit [Member] | Loss Adjustment Expenses Recognized In 2021 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Incurred claims and claim adjustment expenses related to current year	54,385
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 26,649
Cumulative number of reported claims | claim	6,195
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to current year	$ 6,892