Benefits and Pension Plans - Changes in Plan Components (Details) - USD ($) $ in Thousands	12 Months Ended
	Aug. 31, 2020	Aug. 31, 2019	Aug. 31, 2018
Change in benefit obligation
Projected benefit obligation at beginning of year	$ 20,087	$ 21,860	$ 22,673
Service cost	295	283	283
Interest cost	451	696	629
Actuarial (gain) loss	2,253	995	17
Benefits paid	(2,423)	(3,747)	(1,742)
Projected benefit obligation at end of year	20,663	20,087	21,860
Change in plan assets
Fair value of plan assets at beginning of year	7,859	9,855	9,003
Actual return on plan assets	868	181	509
Employer contribution	1,864	1,570	2,085
Benefits paid	(2,423)	(3,747)	(1,742)
Fair value of plan assets at end of year	8,168	7,859	9,855
Funded status
Funded status at end of year	(12,495)	(12,228)	(12,005)
Amounts recognized in consolidated balance sheets
Noncurrent assets			301
Current liabilities	(1,565)	(1,743)	(1,570)
Noncurrent liabilities	(10,930)	(10,485)	(10,736)
Net amount recognized in consolidated balance sheets	(12,495)	(12,228)	(12,005)
Actuarial present value of benefit obligation and funded status
Accumulated benefit obligations	18,307	18,244	20,075
Projected benefit obligations	20,663	20,087	21,858
Plan assets at fair value	8,168	7,859	9,855
Amounts recognized in accumulated other comprehensive income
Prior service cost	44	47	54
Net actuarial loss	10,595	9,638	9,377
Adjustment to pre-tax accumulated other comprehensive income	10,639	9,685	9,431
Other changes in plan assets and benefit obligations recognized in other comprehensive income
Net (gain)/loss	711	1,863	(704)
Amortization of loss	(664)	(472)	(484)
Supplemental plan assumption change	1,065	(620)	676
Amortization of prior service cost	(3)	(3)	(3)
Effect of settlement on accumulated other comprehensive income	(155)	(511)
Total recognized in other comprehensive income	954	257	(515)
Net periodic pension cost	1,178	1,537	937
Total recognized in net periodic pension cost and other comprehensive income	2,132	1,794	422
Estimated amounts that will be amortized from accumulated comprehensive income over the next fiscal year
Prior service cost	3	3	3
Net actuarial loss	656	500	475
Components of net periodic benefit cost
Service cost	295	283	283
Interest cost	451	696	629
Expected return on plan assets	(390)	(428)	(462)
Amortization of prior service cost	3	3	3
Amortization of accumulated loss	664	472	484
Curtailment and settlement loss	155	511
Net periodic benefit cost	1,178	$ 1,537	$ 937
NEPTCO
Change in plan assets
Fair value of plan assets at end of year	$ 0
NEPTCO | Union Employees
Pensions and Other Postretirement Benefits
Period before retirement for determination of employee's average compensation	5 years