Employee Benefits Salary Continuation Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
San Francisco Salary Continuation Plan [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Postemployment Benefits, Period Expense	$ 0.1	$ 0.1	$ 0.1
Postemployment Benefits Liability	1.0	1.1
Cash Surrender Value of Life Insurance	6.1	6.3
Southern California Salary Continuation Plan [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Postemployment Benefits, Period Expense	0.1	0.1	$ 0.1
Postemployment Benefits Liability	1.7	1.9
Cash Surrender Value of Life Insurance	$ 4.9	$ 4.8