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, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	$ 1,745,170
Reinsurance recoverables on unpaid losses	76,100
Insurance lines other than short-duration	629
Unallocated claims adjustment expenses	99,356
Unallocated claims adjustment expenses, aggregate reconciling items	99,985
Total gross loss and loss adjustment expense reserves	1,921,255	$ 1,829,412	$ 1,510,613	$ 1,290,248
Property insurance product line, automobile [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	1,439,861
Reinsurance recoverables on unpaid losses	22,060
Property insurance product line, homeowners' [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	182,731
Reinsurance recoverables on unpaid losses	52,317
Property Insurance Product Line, WAIC Automobile [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	16,576
Other Short-duration Insurance Product Line [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	106,002
Reinsurance recoverables on unpaid losses	$ 1,723