Reinsurance (Reinsurance recoverables by reinsurer) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Ceded Credit Risk [Line Items]
Allowance for reinsurance recoverable	$ 5,153	$ 4,997
Reinsurance Recoverable [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverable	$ 465,668	$ 373,657
Percentage of total reinsurance recoverable	100.00%	100.00%
Reinsurance Recoverable [Member] | A Minus Or Better Rating [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverable	$ 461,369	$ 368,638
Percentage of total reinsurance recoverable	99.10%	98.70%
Reinsurance Recoverable [Member] | Top 10 reinsurers [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverable	$ 395,308	$ 303,108
Percentage of total reinsurance recoverable	84.90%	81.10%
Reinsurance Recoverable [Member] | Top 10 reinsurers [Member] | Lloyds Syndicates [Member] | A (plus) [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverable	$ 84,419	$ 66,356
Percentage of total reinsurance recoverable	18.20%	17.80%
Reinsurance Recoverable [Member] | Top 10 reinsurers [Member] | Swiss Re [Member] | AA- [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverable	$ 84,044	$ 83,048
Percentage of total reinsurance recoverable	18.10%	22.20%
Reinsurance Recoverable [Member] | Top 10 reinsurers [Member] | Fully Collateralized [Member] | NR [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverable	$ 83,088
Percentage of total reinsurance recoverable	17.80%
Reinsurance Recoverable [Member] | Top 10 reinsurers [Member] | Hannover Re [Member] | AA- [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverable	$ 50,603	$ 43,765
Percentage of total reinsurance recoverable	10.90%	11.70%
Reinsurance Recoverable [Member] | Top 10 reinsurers [Member] | Everest Re [Member] | A (plus) [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverable	$ 36,912	$ 43,060
Percentage of total reinsurance recoverable	7.90%	11.50%
Reinsurance Recoverable [Member] | Top 10 reinsurers [Member] | Munich Re [Member] | AA- [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverable	$ 18,214	$ 18,707
Percentage of total reinsurance recoverable	3.90%	5.00%
Reinsurance Recoverable [Member] | Top 10 reinsurers [Member] | Transatlantic Re [Member] | A (plus) [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverable	$ 10,593	$ 11,923
Percentage of total reinsurance recoverable	2.30%	3.20%
Reinsurance Recoverable [Member] | Top 10 reinsurers [Member] | Hamilton Re [Member] | A- Rating [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverable	$ 10,343	$ 10,898
Percentage of total reinsurance recoverable	2.20%	2.90%
Reinsurance Recoverable [Member] | Top 10 reinsurers [Member] | Toa Re [Member] | A (plus) [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverable	$ 9,510	$ 6,330
Percentage of total reinsurance recoverable	2.00%	1.70%
Reinsurance Recoverable [Member] | Top 10 reinsurers [Member] | National Indemnity Company [Member] | AA (plus) [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverable	$ 7,582	$ 10,293
Percentage of total reinsurance recoverable	1.60%	2.80%
Reinsurance Recoverable [Member] | Top 10 reinsurers [Member] | XL Re [Member] | A (plus) [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverable		$ 8,728
Percentage of total reinsurance recoverable		2.30%
Reinsurance Recoverable [Member] | Other Reinsurers Balances Greater Than One Million Dollars [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverable	$ 66,944	$ 61,222
Percentage of total reinsurance recoverable	14.40%	16.40%
Reinsurance Recoverable [Member] | Other Reinsurers Balances Less Than One Million Dollars [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverable	$ 3,416	$ 9,327
Percentage of total reinsurance recoverable	0.70%	2.50%