Retrocession Arrangements and Reinsurance Ceded Receivables Retrocession Arrangements and Reinsurance Ceded Receivables (Ceded Reinsurance Receivable Assets) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 711,463	$ 578,206
Reinsurance Recoverables, Percentage of Total	100.00%	100.00%
Other Reinsurers [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 153,963	$ 160,285
Reinsurance Recoverables, Percentage of Total	21.60%	27.60%
AM Best, A+ Rating [Member] | Reinsurer A [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 201,915	$ 210,996
Reinsurance Recoverables, Percentage of Total	28.40%	36.50%
AM Best, A+ Rating [Member] | Reinsurer B [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 193,294	$ 45,541
Reinsurance Recoverables, Percentage of Total	27.20%	7.90%
AM Best, A+ Rating [Member] | Reinsurer C [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 73,148	$ 74,412
Reinsurance Recoverables, Percentage of Total	10.30%	12.90%
AM Best, A Rating [Member] | Reinsurer E [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 45,464	$ 43,818
Reinsurance Recoverables, Percentage of Total	6.40%	7.60%
AM Best, A++ Rating [Member] | Reinsurer D [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 43,679	$ 43,154
Reinsurance Recoverables, Percentage of Total	6.10%	7.50%