MERCHANDISE TRUSTS - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2021 USD ($) security	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)
West Virginia Trust Receivable
Schedule Of Available For Sale Securities [Line Items]
Trust assets, fair value	$ 10,100,000		$ 10,000,000
Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Percentage of VIE for cancellable state	50.30%
Merchandise Trusts | Variable Interest Entity, Primary Beneficiary
Schedule Of Available For Sale Securities [Line Items]
Trust assets, fair value	$ 540,034,000		516,284,000
Purchases of available for sale securities	21,600,000	$ 13,200,000
Sales, maturities and paydowns of available for sale securities	4,900,000	$ 11,100,000
Other than temporary impairments loss	$ 136,000
Merchandise Trusts | Variable Interest Entity, Primary Beneficiary | Other Than Temporarily Impaired Securities
Schedule Of Available For Sale Securities [Line Items]
Number of securities that incurred other than temporary impairment losses | security	6
Trust assets, cost	$ 300,000
Trust assets, fair value	200,000
Other than temporary impairments loss	100,000
Other than temporary impairment to investment portfolio	0
Merchandise Trusts | West Virginia Trust Receivable | Variable Interest Entity, Primary Beneficiary
Schedule Of Available For Sale Securities [Line Items]
Trust assets, fair value	$ 10,090,000		$ 9,969,000