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Benefit Plans Actuarial Calculation Assumptions (Details)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Pension Plan [Member]
     
Defined Benefit Plan Disclosure [Line Items]      
Net periodic benefit cost, discount rate 4.34% 5.48%  
Net periodic benefit cost, expected return on plan assets 7.00% 7.00%  
Net periodic benefit cost, rate of compensation increase 4.00% 4.00% 4.00%
Benefit obligations, discount rate 3.92% 4.34%  
Benefit obligations, rate of compensation increase 4.00% 4.00%  
Other Postretirement Benefit Plan [Member]
     
Defined Benefit Plan Disclosure [Line Items]      
Net periodic benefit cost, discount rate 4.25% 5.40% 5.83%
Net periodic benefit cost, expected return on plan assets 7.00% 7.00% 8.00%
Benefit obligations, discount rate 3.80% 4.25%  
Maximum [Member] | Pension Plan [Member]
     
Defined Benefit Plan Disclosure [Line Items]      
Net periodic benefit cost, discount rate     5.92% [1]
Net periodic benefit cost, expected return on plan assets     8.00% [1]
Minimum [Member] | Pension Plan [Member]
     
Defined Benefit Plan Disclosure [Line Items]      
Net periodic benefit cost, discount rate     5.51% [1]
Net periodic benefit cost, expected return on plan assets     7.00% [1]
[1] San Jose Water Company updated its expected return on plan assets assumption in November 2010 to reflect the approved redistribution of investments held between equity and fixed income securities in the plan asset portfolio. As a result, San Jose Water Company remeasured the plan assets and benefit obligation as of that date and the discount rate applied was updated accordingly.