Fair Value Measurements (Tables)

6 Months Ended

Mar. 31, 2018

Fair Value Disclosures [Abstract]

Schedule of Financial Assets and Financial Liabilities that are Measured at Fair Value on a Recurring Basis

The following table presents, on a gross basis, our derivative assets and liabilities, including both current and noncurrent portions, that are measured at fair value on a recurring basis within the fair value hierarchy, as of March 31, 2018, September 30, 2017 and March 31, 2017:

	Asset (Liability)
	Level 1			Level 2			Level 3		Total
March 31, 2018:
Assets:
Commodity contracts	$	1,042		$	9		$	—	$	1,051
Liabilities:
Commodity contracts	$	(582	)	$	(7	)	$	—	$	(589	)
September 30, 2017:
Assets:
Commodity contracts	$	1,735		$	72		$	—	$	1,807
Liabilities:
Commodity contracts	$	(1,447	)	$	(73	)	$	—	$	(1,520	)
March 31, 2017:
Assets:
Commodity contracts	$	2,157		$	—		$	—	$	2,157
Liabilities:
Commodity contracts	$	(133	)	$	(19	)	$	—	$	(152	)

Schedule of Carrying Amount and Estimated Fair Value of Long-term Debt

The carrying amount and estimated fair value of our long-term debt (including current maturities but excluding unamortized debt issuance costs) at March 31, 2018, September 30, 2017 and March 31, 2017 were as follows:

	March 31, 2018		September 30, 2017		March 31, 2017
Carrying amount	$	838,437	$	755,000	$	775,000
Estimated fair value	$	871,853	$	791,378	$	801,675