Retrocession Arrangements and Reinsurance Ceded Receivables Retrocession Arrangements and Reinsurance Ceded Receivables (Ceded Reinsurance Receivable Assets) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 661,185	$ 578,206
Reinsurance Recoverables, Percentage of Total	100.00%	100.00%
Other Reinsurers [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 111,090	$ 160,285
Reinsurance Recoverables, Percentage of Total	16.90%	27.60%
AM Best, A+ Rating [Member] | Reinsurer A [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 199,261	$ 45,541
Reinsurance Recoverables, Percentage of Total	30.10%	7.90%
AM Best, A+ Rating [Member] | Reinsurer B [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 192,553	$ 210,996
Reinsurance Recoverables, Percentage of Total	29.10%	36.50%
AM Best, A+ Rating [Member] | Reinsurer C [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 73,692	$ 74,412
Reinsurance Recoverables, Percentage of Total	11.10%	12.90%
AM Best, A Rating [Member] | Reinsurer E [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 43,044	$ 43,818
Reinsurance Recoverables, Percentage of Total	6.50%	7.60%
AM Best, A++ Rating [Member] | Reinsurer D [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 41,545	$ 43,154
Reinsurance Recoverables, Percentage of Total	6.30%	7.50%