Common Stock	3 Months Ended
Mar. 31, 2018
Text Block [Abstract]
Common Stock	Note 6 – Common Stock On March 29, 2017, the Company filed with the Securities Exchange Commission (“SEC”) an automatic shelf registration statement on Form S-3 (File No. 333-217018), which became effective upon filing, for the offer and sale of up to $150 million of common stock from time to time in at-the-market offerings under the prospectus included therein and in accordance with the Sales Agency Agreement, dated March 29, 2017, between the Company and BNY Mellon Capital Markets, LLC (the “Equity Shelf Program”). During the three months ending March 31, 2018, the Company sold, through the continuous equity offering program with BNY Mellon Capital Markets, LLC as agent, an aggregate of 137,300 shares of the Company’s common stock in the open market at a weighted average price of $67.00 per share, resulting in proceeds to the Company of $9,107,664, net of $91,997 in agent commissions. During the twelve months ended March 31, 2018, the Company sold, through this continuous equity offering program with the same party acting as agent, an aggregate of 643,007 shares of the Company’s common stock in the open market at a weighted average price of $79.28 per share, resulting in proceeds to the Company of $50,466,691, net of $509,765 in agent commissions. As of March 31, 2018, the Company had up to $99,023,545 of common stock available for sale under the program. Net proceeds from the sale of shares of common stock under the Equity Shelf Program are intended for general corporate purposes, including the acquisition of property for the construction, completion, extension or improvement of pipeline systems and facilities located in and around the communities served by Southwest. During the three months ended March 31, 2018, the Company issued approximately 77,000 shares of common stock through the Restricted Stock/Unit Plan and Management Incentive Plan. Also during the quarter ended March 31, 2018, the Company issued 33,000 shares of common stock through the Dividend Reinvestment and Stock Purchase Plan (“DRSPP”), raising approximately $2 million.

Note 6 – Common Stock

On March 29, 2017, the Company filed with the Securities Exchange Commission (“SEC”) an automatic shelf registration statement on Form S-3 (File No. 333-217018), which became effective upon filing, for the offer and sale of up to $150 million of common stock from time to time in at-the-market offerings under the prospectus included therein and in accordance with the Sales Agency Agreement, dated March 29, 2017, between the Company and BNY Mellon Capital Markets, LLC (the “Equity Shelf Program”). During the three months ending March 31, 2018, the Company sold, through the continuous equity offering program with BNY Mellon Capital Markets, LLC as agent, an aggregate of 137,300 shares of the Company’s common stock in the open market at a weighted average price of $67.00 per share, resulting in proceeds to the Company of $9,107,664, net of $91,997 in agent commissions. During the twelve months ended March 31, 2018, the Company sold, through this continuous equity offering program with the same party acting as agent, an aggregate of 643,007 shares of the Company’s common stock in the open market at a weighted average price of $79.28 per share, resulting in proceeds to the Company of $50,466,691, net of $509,765 in agent commissions. As of March 31, 2018, the Company had up to $99,023,545 of common stock available for sale under the program. Net proceeds from the sale of shares of common stock under the Equity Shelf Program are intended for general corporate purposes, including the acquisition of property for the construction, completion, extension or improvement of pipeline systems and facilities located in and around the communities served by Southwest.

During the three months ended March 31, 2018, the Company issued approximately 77,000 shares of common stock through the Restricted Stock/Unit Plan and Management Incentive Plan.

Also during the quarter ended March 31, 2018, the Company issued 33,000 shares of common stock through the Dividend Reinvestment and Stock Purchase Plan (“DRSPP”), raising approximately $2 million.