Reserves for Losses and Loss Adjustment Expenses (Incurred and Paid Claims Development - Programs) (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
Specialty Programs Business Unit [Member]
Liability For Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Total incurred	30,139
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Total paid	24,495
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	5,644
Specialty Programs Business Unit [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		196	196	$ 196	$ 196	$ 196	$ 196	$ 196	$ 196	317
Incurred claims and claim adjustment expenses related to current year	196
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	196	196	196	196	196	196	196	196	196	$ 196
Specialty Programs 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		2,045	2,045	2,045	2,045	3,885	2,045	2,045	3,001
Incurred claims and claim adjustment expenses related to current year	$ 2,045
Cumulative number of reported claims | claim	3
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 2,045	2,045	2,045	2,045	2,045	2,045	2,045	2,045	$ 2,045
Specialty Programs 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		2,302	2,302	2,302	2,076	1,561	2,543	1,595
Incurred claims and claim adjustment expenses related to current year	$ 2,302
Cumulative number of reported claims | claim	2
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 2,302	2,302	2,302	2,302	2,076	1,561	1,561	$ 1,489
Specialty Programs 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		1,575	1,575	1,575	2,039	666	1,623
Incurred claims and claim adjustment expenses related to current year	$ 1,575
Cumulative number of reported claims | claim	5
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 1,575	1,575	1,575	1,575	1,575	1,502	$ 758
Specialty Programs 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		752	752	752	1,629	1,683
Incurred claims and claim adjustment expenses related to current year	$ 752
Cumulative number of reported claims | claim	2
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 752	752	752	752	1,629	$ 1,515
Specialty Programs 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		1,178	1,178	1,200	478
Incurred claims and claim adjustment expenses related to current year	$ 1,178
Cumulative number of reported claims | claim	1
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 1,178	1,178	1,178	1,139	$ 1,139
Specialty Programs 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		1,801	1,775	955
Incurred claims and claim adjustment expenses related to current year	1,982
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 15
Cumulative number of reported claims | claim	65
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 1,967	1,551	1,556	$ 36
Specialty Programs 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		4,368	3,598
Incurred claims and claim adjustment expenses related to current year	4,222
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 104
Cumulative number of reported claims | claim	770
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 3,778	1,290	$ 911
Specialty Programs 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		5,407
Incurred claims and claim adjustment expenses related to current year	9,150
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 809
Cumulative number of reported claims | claim	977
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to prior years	$ 7,794	$ 4,501
Specialty Programs Business Unit [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	6,737
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 2,130
Cumulative number of reported claims | claim	652
Liability For Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract]
Paid claims and allocated claim adjustment expenses related to current year	$ 2,908