Reinsurance (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2011	Dec. 31, 2010
Reinsurance recoverables by reinsurer
Reinsurance Recoverable	$ 470,659	$ 311,130
Percentage of total	100.00%	100.00%
Reinsurance (Textuals) [Abstract]
Incurred but not reported recoverable	98,321	146,519
Provision for uncollectible reinsurance relating to losses recoverable	6,200	5,652
Top 10 reinsurers [Member]
Reinsurance recoverables by reinsurer
Reinsurance Recoverable	340,391	222,420
Percentage of total	72.30%	71.50%
Percentage of top 10 reinsurers reinsurance recoverable	100.00%	100.00%
Top 10 reinsurers [Member] | Lloyd's Syndicates [Member] | A+ [Member]
Reinsurance recoverables by reinsurer
Reinsurance Recoverable	74,882	60,716
Percentage of top 10 reinsurers reinsurance recoverable	22.00%	27.20%
Top 10 reinsurers [Member] | Fully Collateralized Reinsurers [Member] | NR [Member]
Reinsurance recoverables by reinsurer
Reinsurance Recoverable	20,396	23,750
Percentage of top 10 reinsurers reinsurance recoverable	6.00%	10.70%
Top 10 reinsurers [Member] | Montpelier Re [Member] | A- [Member]
Reinsurance recoverables by reinsurer
Reinsurance Recoverable		20,000
Percentage of top 10 reinsurers reinsurance recoverable		9.00%
Top 10 reinsurers [Member] | Hannover Re [Member] | AA- [Member]
Reinsurance recoverables by reinsurer
Reinsurance Recoverable	35,757	32,392
Percentage of top 10 reinsurers reinsurance recoverable	10.50%	14.60%
Top 10 reinsurers [Member] | Munich Re [Member] | AA- [Member]
Reinsurance recoverables by reinsurer
Reinsurance Recoverable	15,730	17,411
Percentage of top 10 reinsurers reinsurance recoverable	4.60%	7.80%
Top 10 reinsurers [Member] | Transatlantic Re [Member] | A+ [Member]
Reinsurance recoverables by reinsurer
Reinsurance Recoverable	17,049	13,758
Percentage of top 10 reinsurers reinsurance recoverable	5.00%	6.20%
Top 10 reinsurers [Member] | Everest Re [Member] | A+ [Member]
Reinsurance recoverables by reinsurer
Reinsurance Recoverable	29,812	16,611
Percentage of top 10 reinsurers reinsurance recoverable	8.80%	7.50%
Top 10 reinsurers [Member] | Tokio Millennium Re [Member] | AA [Member]
Reinsurance recoverables by reinsurer
Reinsurance Recoverable		11,980
Percentage of top 10 reinsurers reinsurance recoverable		5.40%
Top 10 reinsurers [Member] | Tokio Marine / Tokio Millennium [Member] | AA- [Member]
Reinsurance recoverables by reinsurer
Reinsurance Recoverable	26,106
Percentage of top 10 reinsurers reinsurance recoverable	7.70%
Top 10 reinsurers [Member] | Allianz [Member] | AA [Member]
Reinsurance recoverables by reinsurer
Reinsurance Recoverable	69,464	14,184
Percentage of top 10 reinsurers reinsurance recoverable	20.30%	6.40%
Top 10 reinsurers [Member] | Platinum Re [Member] | A [Member]
Reinsurance recoverables by reinsurer
Reinsurance Recoverable		11,618
Percentage of top 10 reinsurers reinsurance recoverable		5.20%
Top 10 reinsurers [Member] | Manulife [Member] | AA- [Member]
Reinsurance recoverables by reinsurer
Reinsurance Recoverable	35,000
Percentage of top 10 reinsurers reinsurance recoverable	10.30%
Top 10 reinsurers [Member] | Odyssey Reinsurance Company [Member] | A- [Member]
Reinsurance recoverables by reinsurer
Reinsurance Recoverable	16,195
Percentage of top 10 reinsurers reinsurance recoverable	4.80%
Other reinsurers' balances greater than $1 million
Reinsurance recoverables by reinsurer
Reinsurance Recoverable	119,899	80,221
Percentage of total	25.50%	25.80%
Other reinsurers' balances less than $1 million
Reinsurance recoverables by reinsurer
Reinsurance Recoverable	$ 10,369	$ 8,489
Percentage of total	2.20%	2.70%
"A- or better rating" [Member]
Reinsurance (Textuals) [Abstract]
Percentage of Total	99.10%