    <SEC-DOCUMENT>0001193125-20-250247-index.html : 20201026
    <SEC-HEADER>0001193125-20-250247.hdr.sgml : 20201026
    <ACCEPTANCE-DATETIME>20200921164558
    ACCESSION NUMBER:		0001193125-20-250247
    CONFORMED SUBMISSION TYPE:	8-K
    PUBLIC DOCUMENT COUNT:		19
    CONFORMED PERIOD OF REPORT:	20200915
    ITEM INFORMATION:		Entry into a Material Definitive Agreement
    ITEM INFORMATION:		Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant
    ITEM INFORMATION:		Financial Statements and Exhibits
    FILED AS OF DATE:		20200921
    DATE AS OF CHANGE:		20200921

    FILER:

    	COMPANY DATA:
    		COMPANY CONFORMED NAME:			UNITIL CORP
    		CENTRAL INDEX KEY:			0000755001
    		STANDARD INDUSTRIAL CLASSIFICATION:	ELECTRIC & OTHER SERVICES COMBINED [4931]
    		IRS NUMBER:				020381573
    		STATE OF INCORPORATION:			NH
    		FISCAL YEAR END:			1231

    	FILING VALUES:
    		FORM TYPE:		8-K
    		SEC ACT:		1934 Act
    		SEC FILE NUMBER:	001-08858
    		FILM NUMBER:		201186920

    	BUSINESS ADDRESS:
    		STREET 1:		6 LIBERTY LANE WEST
    		CITY:			HAMPTON
    		STATE:			NH
    		ZIP:			03842
    		BUSINESS PHONE:		6037736504

    	MAIL ADDRESS:
    		STREET 1:		6 LIBERTY LANE WEST
    		CITY:			HAMPTON
    		STATE:			NH
    		ZIP:			03842
    </SEC-HEADER>
    <DOCUMENT>
    <TYPE>8-K
    <SEQUENCE>1
    <FILENAME>d923021d8k.htm
    <DESCRIPTION>8-K
    <TEXT>
    Document 1 - file: d923021d8k.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-4.1
    <SEQUENCE>2
    <FILENAME>d923021dex41.htm
    <DESCRIPTION>EX-4.1
    <TEXT>
    Document 2 - file: d923021dex41.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-4.2
    <SEQUENCE>3
    <FILENAME>d923021dex42.htm
    <DESCRIPTION>EX-4.2
    <TEXT>
    Document 3 - file: d923021dex42.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-4.3
    <SEQUENCE>4
    <FILENAME>d923021dex43.htm
    <DESCRIPTION>EX-4.3
    <TEXT>
    Document 4 - file: d923021dex43.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-4.4
    <SEQUENCE>5
    <FILENAME>d923021dex44.htm
    <DESCRIPTION>EX-4.4
    <TEXT>
    Document 5 - file: d923021dex44.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-4.5
    <SEQUENCE>6
    <FILENAME>d923021dex45.htm
    <DESCRIPTION>EX-4.5
    <TEXT>
    Document 6 - file: d923021dex45.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-4.6
    <SEQUENCE>7
    <FILENAME>d923021dex46.htm
    <DESCRIPTION>EX-4.6
    <TEXT>
    Document 7 - file: d923021dex46.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-4.7
    <SEQUENCE>8
    <FILENAME>d923021dex47.htm
    <DESCRIPTION>EX-4.7
    <TEXT>
    Document 8 - file: d923021dex47.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-101.SCH
    <SEQUENCE>9
    <FILENAME>utl-20200915.xsd
    <DESCRIPTION>XBRL TAXONOMY EXTENSION SCHEMA
    <TEXT>
    Document 9 - file: utl-20200915.xsd

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-101.LAB
    <SEQUENCE>10
    <FILENAME>utl-20200915_lab.xml
    <DESCRIPTION>XBRL TAXONOMY EXTENSION LABEL LINKBASE
    <TEXT>
    Document 10 - file: utl-20200915_lab.xml

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-101.PRE
    <SEQUENCE>11
    <FILENAME>utl-20200915_pre.xml
    <DESCRIPTION>XBRL TAXONOMY EXTENSION PRESENTATION LINKBASE
    <TEXT>
    Document 11 - file: utl-20200915_pre.xml

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>12
    <FILENAME>g923021page180a.jpg
    <DESCRIPTION>GRAPHIC
    <TEXT>
    Document 12 - file: g923021page180a.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>13
    <FILENAME>g923021pagr180b.jpg
    <DESCRIPTION>GRAPHIC
    <TEXT>
    Document 13 - file: g923021pagr180b.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>XML
    <SEQUENCE>14
    <FILENAME>d923021d8k_htm.xml
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 14 - file: d923021d8k_htm.html

    Document 14 - RAW XML: d923021d8k_htm.xml

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>XML
    <SEQUENCE>15
    <FILENAME>R1.htm
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 15 - file: R1.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EXCEL
    <SEQUENCE>16
    <FILENAME>Financial_Report.xlsx
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 16 - file: Financial_Report.xlsx

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>XML
    <SEQUENCE>17
    <FILENAME>Show.js
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 17 - file: Show.js

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>XML
    <SEQUENCE>18
    <FILENAME>report.css
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 18 - file: report.css

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>XML
    <SEQUENCE>19
    <FILENAME>FilingSummary.xml
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 19 - file: FilingSummary.html

    Document 19 - RAW XML: FilingSummary.xml

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>JSON
    <SEQUENCE>20
    <FILENAME>MetaLinks.json
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 20 - file: MetaLinks.json

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>ZIP
    <SEQUENCE>21
    <FILENAME>0001193125-20-250247-xbrl.zip
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 21 - file: 0001193125-20-250247-xbrl.zip

    </DOCUMENT>
    </SEC-DOCUMENT>