STOCK-BASED COMPENSATION - NARRATIVE (Details) - USD ($)		12 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance (in shares)		3,473,061.93
Performance Shares, Market Condition Award
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted but not issued (in shares)		31,836	44,576	46,175
Performance Shares, Subject to Performance Conditions
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted but not issued (in shares)		59,341	51,931	69,305
Deferred compensation related to unvested performance shares, period		1 year 8 months 12 days
Performance share awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted but not issued (in shares)	[1]	145,176	156,587	179,916	214,464
Deferred compensation related to unvested restricted and performance shares		$ 3,800,000
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted but not issued (in shares)		44,168	51,154	73,071	81,492
Deferred compensation related to unvested restricted and performance shares		$ 612,964
Deferred compensation related to unvested performance shares, period		2 years
Vesting September 30, 2020 | Performance Shares, Subject to Performance Conditions
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted but not issued (in shares)		29,608
Vesting Annually Over Three Year Period Beginning September 30, 2018 | Performance Shares, Subject to Performance Conditions
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted but not issued (in shares)		29,733
Award vesting period		3 years
Vesting September 30, 2019 | Performance Shares, Subject to Performance Conditions
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted but not issued (in shares)			25,806
Vesting Annually Over Three Year Period Beginning September 30, 2017 | Performance Shares, Subject to Performance Conditions
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted but not issued (in shares)			26,125
Award vesting period			3 years
Vesting September 30, 2018 | Performance Shares, Subject to Performance Conditions
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted but not issued (in shares)				38,789
Vesting Annually Over Three Year Period Beginning September 30, 2016 | Performance Shares, Subject to Performance Conditions
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted but not issued (in shares)				30,516
Award vesting period				3 years
Vesting Annually Over Three Year Period Beginning October 15, 2018 | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted but not issued (in shares)		27,949
Award vesting period		3 years
Vesting Annually Over Three Year Period Beginning October 2017 | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted but not issued (in shares)			22,591
Award vesting period			3 years
Vesting Annually Over Three Year Period Beginning May 8, 2018 | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted but not issued (in shares)			6,143
Award vesting period			3 years
Vesting Annually Over a Three Year Period Beginning in October 2016 | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted but not issued (in shares)				41,909
Award vesting period				3 years
NJR 2007 Stock Award And Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted but not issued (in shares)			914,169
NJR 2017 Stock Award And Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares authorized for issuance (in shares)		3,135,000

[1] The number of common shares issued related to certain performance shares may range from zero to 150 percent of the number of shares shown in the table above based on the Company’s achievement of performance goals.