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Name:	us-gaap_MarketableSecuritiesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Marketable Securities and Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Marketable Securities [Line Items]
Net unrealized gains	$ 1,908,000	$ 1,190,000
BlawKnox Paver [Member]
Marketable Securities [Line Items]
Liquidity On Investments			$ 17,000,000.0