Impairment - Wood Treatment - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Impaired Long-Lived Assets Held and Used [Line Items]
Goodwill impairment loss	$ 4,081
Goodwill	721,621		$ 718,647
Recognized tax benefit	(7,546)	$ (10,881)
Wood Treatment
Impaired Long-Lived Assets Held and Used [Line Items]
Long-lived asset impairment	3,266
Intangible assets	0
Goodwill impairment loss	4,081
Goodwill	30,900
Recognized tax benefit	$ 606