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, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	$ 1,820,077
Reinsurance recoverables on unpaid losses	54,460
Insurance lines other than short-duration	676
Unallocated claims adjustment expenses	116,091
Unallocated claims adjustment expenses, aggregate reconciling items	116,767
Total gross loss and loss adjustment expense reserves	1,991,304	$ 1,921,255	$ 1,829,412	$ 1,510,613
Property insurance product line, automobile [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	1,442,694
Reinsurance recoverables on unpaid losses	18,187
Property insurance product line, homeowners' [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	233,189
Reinsurance recoverables on unpaid losses	35,214
Property Insurance Product Line, WAIC Automobile [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	13,903
Other Short-duration Insurance Product Line [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	130,291
Reinsurance recoverables on unpaid losses	$ 1,059