Reinsurance (Ceded Reinsurance Receivable Assets) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 863,027	$ 757,572
Reinsurance Recoverables, Percentage of Total	100.00%	100.00%
Other Reinsurers [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 128,301	$ 114,723
Reinsurance Recoverables, Percentage of Total	14.90%	15.20%
AM Best, A+ Rating [Member] | Reinsurer A [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 358,845	$ 303,036
Reinsurance Recoverables, Percentage of Total	41.60%	40.00%
AM Best, A+ Rating [Member] | Reinsurer B [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 201,011	$ 193,324
Reinsurance Recoverables, Percentage of Total	23.30%	25.50%
AM Best, A+ Rating [Member] | Reinsurer E [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 40,816	$ 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	$ 76,807	$ 69,885
Reinsurance Recoverables, Percentage of Total	8.90%	9.20%
AM Best, A++ Rating [Member] | Reinsurer D [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 57,247	$ 36,600
Reinsurance Recoverables, Percentage of Total	6.60%	4.80%