General (Policies)	3 Months Ended
General (Policies)	Mar. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Accounting, Policy	The unaudited interim financial information has been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) and in accordance with the instructions for Form 10-Q and Rule 10-01 of Regulation S-X promulgated by the Securities and Exchange Commission (the “SEC”). The Notes to Consolidated Financial Statements in SJW Corp.'s 2014 Annual Report on Form 10-K should be read with the accompanying unaudited condensed consolidated financial statements.
Earnings Per Share, Policy	Basic earnings per share is calculated using income available to common shareholders, divided by the weighted average number of shares outstanding during the period. Diluted earnings per share is calculated using income available to common shareholders divided by the weighted average number of shares of common stock including both shares outstanding and shares potentially issuable in connection with deferred restricted common stock awards under SJW Corp.'s Long-Term Incentive Plan (as amended, the “Incentive Plan”) and shares potentially issuable under the 2014 Employee Stock Purchase Plan (“ESPP”).

Disclosure of accounting policy for computing basic and diluted earnings or loss per share for each class of common stock and participating security. Addresses all significant policy factors, including any antidilutive items that have been excluded from the computation and takes into account stock dividends, splits and reverse splits that occur after the balance sheet date of the latest reporting period but before the issuance of the financial statements.

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