Losses And Loss Adjustment Expense Reserves - Reconciliation of the Disclosure of Incurred and Paid Claims Development to the Loss and Loss Adjustment Expense Reserves (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	$ 1,359,898
Reinsurance recoverables on unpaid losses	64,001
Insurance lines other than short-duration	1,183
Unallocated claims adjustment expenses	85,531
Unallocated claims adjustment expenses, aggregate reconciling items	86,714
Total gross loss and loss adjustment expense reserves	1,510,613	$ 1,290,248	$ 1,146,688	$ 1,091,797
Property insurance product line, automobile [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	1,141,300
Reinsurance recoverables on unpaid losses	10,004
Property insurance product line, homeowners' [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	137,195
Reinsurance recoverables on unpaid losses	53,323
Property Insurance Product Line, WAIC Automobile [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	12,076
Other Short-duration Insurance Product Line [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	69,327
Reinsurance recoverables on unpaid losses	$ 674