Employee Retirement Plans - Fair Value of Pension Plan and VEBA Trust Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
VEBA Trust
Defined Benefit Plan Disclosure
Fair value of plan assets	$ 14,771	$ 13,715
Other	409	113
VEBA Trust | S&P 500 Index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	9,318	9,583
Other	0	0
VEBA Trust | Bond index mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	5,044	4,019
Other	0	0
VEBA Trust | Cash equivalents
Defined Benefit Plan Disclosure
Fair value of plan assets	409	113
Other	409	113
VEBA Trust | Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets	14,362	13,602
VEBA Trust | Level 1 | S&P 500 Index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	9,318	9,583
VEBA Trust | Level 1 | Bond index mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	5,044	4,019
VEBA Trust | Level 1 | Cash equivalents
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
VEBA Trust | Level 2
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
VEBA Trust | Level 2 | S&P 500 Index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
VEBA Trust | Level 2 | Bond index mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
VEBA Trust | Level 2 | Cash equivalents
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
VEBA Trust | Level 3
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
VEBA Trust | Level 3 | S&P 500 Index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
VEBA Trust | Level 3 | Bond index mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
VEBA Trust | Level 3 | Cash equivalents
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Pension Benefits
Defined Benefit Plan Disclosure
Fair value of plan assets	498,080	463,432	$ 430,789
Pension Benefits | U.S. Pension Plan
Defined Benefit Plan Disclosure
Fair value of plan assets	498,077	463,432
Other	5,332	17,811
Pension Benefits | U.S. Pension Plan | Total domestic equity investments
Defined Benefit Plan Disclosure
Fair value of plan assets	274,904	250,503
Other	0	0
Pension Benefits | U.S. Pension Plan | S&P 500 Index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	171,600	158,906
Other	0	0
Pension Benefits | U.S. Pension Plan | Small and midcap equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	65,167	43,170
Other	0	0
Pension Benefits | U.S. Pension Plan | Smallcap common stocks
Defined Benefit Plan Disclosure
Fair value of plan assets		11,414
Other		0
Pension Benefits | U.S. Pension Plan | UGI Corporation Common Stock
Defined Benefit Plan Disclosure
Fair value of plan assets	38,137	37,013
Other	0	0
Pension Benefits | U.S. Pension Plan | International index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	61,613	47,324
Other	0	0
Pension Benefits | U.S. Pension Plan | Total fixed income investments
Defined Benefit Plan Disclosure
Fair value of plan assets	161,560	165,605
Other	5,332	17,811
Pension Benefits | U.S. Pension Plan | Bond index mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	156,228	147,794
Other	0	0
Pension Benefits | U.S. Pension Plan | Cash equivalents
Defined Benefit Plan Disclosure
Fair value of plan assets	5,332	17,811
Other	5,332	17,811
Pension Benefits | U.S. Pension Plan | Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets	492,745	445,621
Pension Benefits | U.S. Pension Plan | Level 1 | Total domestic equity investments
Defined Benefit Plan Disclosure
Fair value of plan assets	274,904	250,503
Pension Benefits | U.S. Pension Plan | Level 1 | S&P 500 Index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	171,600	158,906
Pension Benefits | U.S. Pension Plan | Level 1 | Small and midcap equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	65,167	43,170
Pension Benefits | U.S. Pension Plan | Level 1 | Smallcap common stocks
Defined Benefit Plan Disclosure
Fair value of plan assets		11,414
Pension Benefits | U.S. Pension Plan | Level 1 | UGI Corporation Common Stock
Defined Benefit Plan Disclosure
Fair value of plan assets	38,137	37,013
Pension Benefits | U.S. Pension Plan | Level 1 | International index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	61,613	47,324
Pension Benefits | U.S. Pension Plan | Level 1 | Total fixed income investments
Defined Benefit Plan Disclosure
Fair value of plan assets	156,228	147,794
Pension Benefits | U.S. Pension Plan | Level 1 | Bond index mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	156,228	147,794
Pension Benefits | U.S. Pension Plan | Level 1 | Cash equivalents
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Pension Benefits | U.S. Pension Plan | Level 2
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Pension Benefits | U.S. Pension Plan | Level 2 | Total domestic equity investments
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Pension Benefits | U.S. Pension Plan | Level 2 | S&P 500 Index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Pension Benefits | U.S. Pension Plan | Level 2 | Small and midcap equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Pension Benefits | U.S. Pension Plan | Level 2 | Smallcap common stocks
Defined Benefit Plan Disclosure
Fair value of plan assets		0
Pension Benefits | U.S. Pension Plan | Level 2 | UGI Corporation Common Stock
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Pension Benefits | U.S. Pension Plan | Level 2 | International index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Pension Benefits | U.S. Pension Plan | Level 2 | Total fixed income investments
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Pension Benefits | U.S. Pension Plan | Level 2 | Bond index mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Pension Benefits | U.S. Pension Plan | Level 2 | Cash equivalents
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Pension Benefits | U.S. Pension Plan | Level 3
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Pension Benefits | U.S. Pension Plan | Level 3 | Total domestic equity investments
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Pension Benefits | U.S. Pension Plan | Level 3 | S&P 500 Index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Pension Benefits | U.S. Pension Plan | Level 3 | Small and midcap equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Pension Benefits | U.S. Pension Plan | Level 3 | Smallcap common stocks
Defined Benefit Plan Disclosure
Fair value of plan assets		0
Pension Benefits | U.S. Pension Plan | Level 3 | UGI Corporation Common Stock
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Pension Benefits | U.S. Pension Plan | Level 3 | International index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Pension Benefits | U.S. Pension Plan | Level 3 | Total fixed income investments
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Pension Benefits | U.S. Pension Plan | Level 3 | Bond index mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Pension Benefits | U.S. Pension Plan | Level 3 | Cash equivalents
Defined Benefit Plan Disclosure
Fair value of plan assets	$ 0	$ 0