Reinsurance (Ceded Reinsurance Receivable Assets) (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 851,380	$ 757,572
Reinsurance Recoverables, Percentage of Total	100.00%	100.00%
Other Reinsurers [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 127,218	$ 114,723
Reinsurance Recoverables, Percentage of Total	15.00%	15.20%
AM Best, A+ Rating [Member] | Reinsurer A [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 347,916	$ 303,036
Reinsurance Recoverables, Percentage of Total	40.90%	40.00%
AM Best, A+ Rating [Member] | Reinsurer B [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 201,983	$ 193,324
Reinsurance Recoverables, Percentage of Total	23.70%	25.50%
AM Best, A+ Rating [Member] | Reinsurer E [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 40,253	$ 40,004
Reinsurance Recoverables, Percentage of Total	4.70%	5.30%
AM Best, A Rating [Member] | Reinsurer C [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 74,214	$ 69,885
Reinsurance Recoverables, Percentage of Total	8.70%	9.20%
AM Best, A++ Rating [Member] | Reinsurer D [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 59,796	$ 36,600
Reinsurance Recoverables, Percentage of Total	7.00%	4.80%