Summary of Significant Accounting Policies (Narrative) (Details)	12 Months Ended
	Dec. 31, 2016 USD ($) State Subsidiary	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of insurance companies | Subsidiary	14
Number of states in which company operates | State	11
Percentage of direct premiums written as private passenger automobile lines of insurance	77.00%
Percentage of private passenger automobile premiums written in California	84.00%	83.00%	83.00%
Percentage by which dividend income on non redeemable preferred stock, partnership, common stock is partially tax-sheltered	70.00%
Insurance companies security deposits	$ 19,000,000	$ 21,000,000
Deferred policy acquisition cost amortization	562,545,000	539,231,000	$ 526,208,000
Advertising expenses	40,000,000	44,000,000	23,000,000
Impairment charges	0	0	0
Goodwill impairment loss	0	0
Premiums written, net	$ 3,160,000,000	$ 3,000,000,000	$ 2,840,000,000
Options Granted Subsequent To January 1, 2008 [Member]
Summary Of Significant Accounting Policies [Line Items]
Option vesting term, years	4 years
Minimum [Member] | Options Granted Prior To 2008 [Member]
Summary Of Significant Accounting Policies [Line Items]
Option vesting term, years	4 years
Maximum [Member] | Options Granted Prior To 2008 [Member]
Summary Of Significant Accounting Policies [Line Items]
Option vesting term, years	5 years
Building [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful life, in years	30 years
Building [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful life, in years	40 years
Furniture Equipment And Purchase Software [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful life, in years	3 years
Furniture Equipment And Purchase Software [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful life, in years	7 years
Software [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful life, in years	7 years