Loss 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, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	$ 1,555,579
Reinsurance recoverables on unpaid losses	180,859
Insurance lines other than short-duration	1,079
Unallocated claims adjustment expenses	91,895
Unallocated claims adjustment expenses, aggregate reconciling items	92,974
Total gross loss and loss adjustment expense reserves	1,829,412	$ 1,510,613	$ 1,290,248	$ 1,146,688
Property insurance product line, automobile [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	1,294,025
Reinsurance recoverables on unpaid losses	41,316
Property insurance product line, homeowners' [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	154,043
Reinsurance recoverables on unpaid losses	138,096
Property Insurance Product Line, WAIC Automobile [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	17,508
Other Short-duration Insurance Product Line [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	90,003
Reinsurance recoverables on unpaid losses	$ 1,447