Common Stock	6 Months Ended
Jun. 30, 2018
Text Block [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 ending June 30, 2018, the Company sold, through the continuous equity offering program with BNY Mellon Capital Markets, LLC as agent, an aggregate of 748,932 shares of the Company’s common stock in the open market at a weighted average price of $74.10 per share, resulting in proceeds to the Company of $54,940,503 net of $554,954 in agent commissions. During the six months ending June 30, 2018, the Company sold, through the continuous equity offering program with BNY Mellon Capital Markets, LLC as agent, an aggregate of 886,232 shares of the Company’s common stock in the open market at a weighted average price of $73.00 per share, resulting in proceeds to the Company of $64,048,167 net of $646,951 in agent commissions. During the twelve months ended June 30, 2018, the Company sold, through this continuous equity offering program with the same party acting as agent, an aggregate of 1,391,939 shares of the Company’s common stock in the open market at a weighted average price of $76.49 per share, resulting in proceeds to the Company of $105,407,194, net of $1,064,719 in agent commissions. As of June 30, 2018, the Company had up to $43,528,087 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 six months ended June 30, 2018, the Company issued approximately 77,000 shares of common stock through the Restricted Stock/Unit Plan and Management Incentive Plan. Also during the six months ended June 30, 2018, the Company issued 73,000 shares of common stock through the Dividend Reinvestment and Stock Purchase Plan (“DRSPP”), raising approximately $5 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 ending June 30, 2018, the Company sold, through the continuous equity offering program with BNY Mellon Capital Markets, LLC as agent, an aggregate of 748,932 shares of the Company’s common stock in the open market at a weighted average price of $74.10 per share, resulting in proceeds to the Company of $54,940,503 net of $554,954 in agent commissions. During the six months ending June 30, 2018, the Company sold, through the continuous equity offering program with BNY Mellon Capital Markets, LLC as agent, an aggregate of 886,232 shares of the Company’s common stock in the open market at a weighted average price of $73.00 per share, resulting in proceeds to the Company of $64,048,167 net of $646,951 in agent commissions. During the twelve months ended June 30, 2018, the Company sold, through this continuous equity offering program with the same party acting as agent, an aggregate of 1,391,939 shares of the Company’s common stock in the open market at a weighted average price of $76.49 per share, resulting in proceeds to the Company of $105,407,194, net of $1,064,719 in agent commissions. As of June 30, 2018, the Company had up to $43,528,087 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 six months ended June 30, 2018, the Company issued approximately 77,000 shares of common stock through the Restricted Stock/Unit Plan and Management Incentive Plan.

Also during the six months ended June 30, 2018, the Company issued 73,000 shares of common stock through the Dividend Reinvestment and Stock Purchase Plan (“DRSPP”), raising approximately $5 million.