Summary of Significant Accounting Policies (Narrative) (Details)	12 Months Ended
	Dec. 31, 2022 USD ($) State Subsidiary	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Jan. 01, 2020 USD ($)	Dec. 31, 2019 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of insurance companies | Subsidiary	12
Number of states in which company operates | State	11
Percentage of direct premiums written as private passenger automobile lines of insurance	64.00%
Percentage of private passenger automobile premiums written in California	82.00%	87.00%	88.00%
Percentage of portfolio of unadjusted fair values obtained	98.20%
Percentage by which dividend income on non redeemable preferred stock, partnership, common stock is partially tax-sheltered	50.00%
Insurance companies security deposits	$ 14,000,000	$ 15,000,000
Impairment charges	0	0	$ 0
Goodwill impairment loss	0	0
Net premiums written	3,980,000,000	3,860,000,000	3,610,000,000
Reduction in premiums written, net			128,000,000
Reinsurance reimbursable amount	$ 30,000,000
Reinsurance retention policy, threshold loss ratio	73.50%
Reinsurance policy, coverage per occurrence after retention limit	$ 936,000,000
Reinsurance policy, retention limit	60,000,000
Ceded to other companies	(80,950,000)	(65,017,000)	(56,212,000)
Losses and loss adjustment expenses, ceded	$ (13,000,000)	(10,000,000)	(28,000,000)
Vesting term	4 years
Revenue from contract with customer	$ 18,200,000	20,200,000	18,000,000
Cost of goods and services sold	11,000,000	12,800,000	11,800,000
Commission income receivable	1,300,000	1,400,000
Refund liability	800,000	900,000
Capitalized contract cost, net	1,100,000	2,800,000
Capitalized contract cost, accumulated amortization	(4,700,000)	(6,000,000)
Capitalized contract cost, amortization	2,800,000	3,900,000	1,800,000
Ending retained earnings	1,522,131,000	2,140,281,000	2,032,597,000
Retained Earnings
Summary Of Significant Accounting Policies [Line Items]
Ending retained earnings	$ 1,423,184,000	2,041,338,000	1,933,627,000		$ 1,700,674,000
Cumulative Effect, Period of Adoption, Adjustment | Retained Earnings
Summary Of Significant Accounting Policies [Line Items]
Ending retained earnings		0	$ 0		$ (2,014,000)
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13 | Retained Earnings
Summary Of Significant Accounting Policies [Line Items]
Ending retained earnings				$ 2,000,000
Software
Summary Of Significant Accounting Policies [Line Items]
Useful life, in years	7 years
Maximum | Building
Summary Of Significant Accounting Policies [Line Items]
Useful life, in years	40 years
Maximum | Furniture Equipment And Purchase Software
Summary Of Significant Accounting Policies [Line Items]
Useful life, in years	7 years
Minimum | Furniture Equipment And Purchase Software
Summary Of Significant Accounting Policies [Line Items]
Useful life, in years	3 years
Private Equity Funds
Summary Of Significant Accounting Policies [Line Items]
Unfunded commitments	$ 9,000,000	$ 32,000,000