Reserves for Unpaid Losses and Loss Adjustment Expenses (Incurred and Paid Claims Development – Commercial Accounts) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) claim	Dec. 31, 2018 USD ($)	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 ($)	Dec. 31, 2010 USD ($)
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total unfavorable net prior year development	$ 60,900	$ 5,953
Incurred claims and claim adjustment expenses related to current year	301,265	250,075
Total incurred	362,165	256,028
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	192,335	232,345
Paid claims and allocated claim adjustment expenses related to current year	127,610	90,640
Total paid	319,945	322,985
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	347,751	305,531	$ 372,488
Commercial Accounts business unit [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total incurred	405,517
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Total paid	355,519
All outstanding liabilities before 2010, net of reinsurance	1,202
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	51,200
Commercial Accounts business unit [Member] | Loss Adjustment Expenses Recognized In 2010 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total unfavorable net prior year development		42,427	42,880	$ 42,175	$ 42,426	$ 43,459	$ 43,164	$ 44,847	$ 45,235	$ 45,263
Incurred claims and claim adjustment expenses related to current year	40,337
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 106
Cumulative number of reported claims | claim	3,143
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 40,040	42,063	40,937	39,706	39,115	37,166	33,428	30,957	28,342	$ 21,304
Commercial Accounts business unit [Member] | Loss Adjustment Expenses Recognized In 2011 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total unfavorable net prior year development		38,585	40,100	40,745	41,081	41,721	45,723	46,540	49,375
Incurred claims and claim adjustment expenses related to current year	38,585
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 199
Cumulative number of reported claims | claim	2,911
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 38,228	38,311	38,253	37,214	36,302	35,333	33,701	30,811	$ 22,002
Commercial Accounts business unit [Member] | Loss Adjustment Expenses Recognized In 2012 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total unfavorable net prior year development		38,669	40,350	41,451	42,632	44,625	48,085	47,194
Incurred claims and claim adjustment expenses related to current year	38,669
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 198
Cumulative number of reported claims | claim	2,703
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 38,211	38,044	37,808	35,943	34,597	32,378	30,096	$ 22,264
Commercial Accounts business unit [Member] | Loss Adjustment Expenses Recognized In 2013 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total unfavorable net prior year development		39,567	42,822	43,917	46,990	47,385	46,413
Incurred claims and claim adjustment expenses related to current year	40,211
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 423
Cumulative number of reported claims | claim	2,800
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 39,329	38,892	37,947	36,225	33,927	29,586	$ 19,386
Commercial Accounts business unit [Member] | Loss Adjustment Expenses Recognized In 2014 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total unfavorable net prior year development		43,673	43,806	43,806	46,470	46,280
Incurred claims and claim adjustment expenses related to current year	42,463
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 562
Cumulative number of reported claims | claim	2,737
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 41,162	39,185	36,775	33,544	31,150	$ 21,322
Commercial Accounts business unit [Member] | Loss Adjustment Expenses Recognized in 2015 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total unfavorable net prior year development		38,385	41,429	42,580	40,966
Incurred claims and claim adjustment expenses related to current year	39,287
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 1,440
Cumulative number of reported claims | claim	2,568
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 35,611	35,238	30,974	28,501	$ 16,557
Commercial Accounts business unit [Member] | Loss Adjustment Expenses Recognized in 2016 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total unfavorable net prior year development		41,983	43,449	43,327
Incurred claims and claim adjustment expenses related to current year	43,111
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 1,518
Cumulative number of reported claims | claim	2,526
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 39,417	35,035	29,456	$ 19,776
Commercial Accounts business unit [Member] | Loss Adjustment Expenses Recognized in 2017 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total unfavorable net prior year development		42,704	40,943
Incurred claims and claim adjustment expenses related to current year	43,579
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 2,793
Cumulative number of reported claims | claim	2,709
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 36,650	28,813	$ 16,644
Commercial Accounts business unit [Member] | Loss Adjustment Expenses Recognized In 2018 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total unfavorable net prior year development		42,898
Incurred claims and claim adjustment expenses related to current year	41,290
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 5,929
Cumulative number of reported claims | claim	2,550
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 29,381	$ 19,233
Commercial Accounts business unit [Member] | Loss Adjustment Expenses Recognized In 2019 [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Incurred claims and claim adjustment expenses related to current year	37,984
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 13,663
Cumulative number of reported claims | claim	2,459
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to current year	$ 17,490