Common Stock	9 Months Ended
Sep. 30, 2018
Equity [Abstract]
Common Stock	Note 6 – Common Stock On March 29, 2017, the Company filed with the 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 ended September 30, 2018, the Company sold, through the Equity Shelf Program, an aggregate of 259,473 shares of the Company’s common stock in the open market at a weighted average price of $78.83 per share, resulting in proceeds to the Company of $20,250,309 net of $204,549 in agent commissions. During the nine months ended September 30, 2018, the Company sold, through the Equity Shelf Program, an aggregate of 1,145,705 shares of the Company’s common stock in the open market at a weighted average price of $74.32 per share, resulting in proceeds to the Company of $84,298,476 net of $851,500 in agent commissions. During the twelve months ended September 30, 2018, the Company sold, through the Equity Shelf Program, an aggregate of 1,504,335 shares of the Company’s common stock in the open market at a weighted average price of $76.55 per share, resulting in proceeds to the Company of $113,998,400, net of $1,151,499 in agent commissions. As of September 30, 2018, the Company had up to $23,073,229 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 nine months ended September 30, 2018, the Company issued approximately 78,000 shares of common stock through the Restricted Stock/Unit Plan and Management Incentive Plan. Also during the nine months ended September 30, 2018, the Company issued 109,000 shares of common stock through the Dividend Reinvestment and Stock Purchase Plan (“DRSPP”), raising approximately $7.8 million.

Note 6 – Common Stock

On March 29, 2017, the Company filed with the 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 ended September 30, 2018, the Company sold, through the Equity Shelf Program, an aggregate of 259,473 shares of the Company’s common stock in the open market at a weighted average price of $78.83 per share, resulting in proceeds to the Company of $20,250,309 net of $204,549 in agent commissions. During the nine months ended September 30, 2018, the Company sold, through the Equity Shelf Program, an aggregate of 1,145,705 shares of the Company’s common stock in the open market at a weighted average price of $74.32 per share, resulting in proceeds to the Company of $84,298,476 net of $851,500 in agent commissions. During the twelve months ended September 30, 2018, the Company sold, through the Equity Shelf Program, an aggregate of 1,504,335 shares of the Company’s common stock in the open market at a weighted average price of $76.55 per share, resulting in proceeds to the Company of $113,998,400, net of $1,151,499 in agent commissions. As of September 30, 2018, the Company had up to $23,073,229 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 nine months ended September 30, 2018, the Company issued approximately 78,000 shares of common stock through the Restricted Stock/Unit Plan and Management Incentive Plan.

Also during the nine months ended September 30, 2018, the Company issued 109,000 shares of common stock through the Dividend Reinvestment and Stock Purchase Plan (“DRSPP”), raising approximately $7.8 million.