Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($)	1 Months Ended	9 Months Ended
	Apr. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments in marketable securities		$ 4,690,000	$ 0
Marketable securities		1,782,000
Supplemental profit sharing plan		4,759,000
Profit Sharing Plan [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Supplemental profit sharing plan		4,800,000		$ 4,800,000
Corporate Owned Life Insurance Policy [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amount sold from available-for-sale securities	$ 2,900,000	3,000,000
Corporate Owned Life Insurance Policy [Member] | Other Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash surrender value		3,000,000
Maximum [Member] | Other Income [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Gain loss on change in fair value of securities		$ 100,000