Leases and Contingencies - Additional Information (Detail) - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019	Jan. 01, 2019
Lessee Lease Description [Line Items]
Operating lease assets (right -of-use assets)	$ 24,779,000	$ 24,779,000	$ 26,385,000	$ 27,500,000
Operating lease liabilities	28,876,000	$ 28,876,000		$ 32,100,000
Lessee, operating lease, existence of option to extend		true
Charges, claims related to litigation	$ 0		$ 0
Minimum [Member]
Lessee Lease Description [Line Items]
Lessee, operating lease, renewal term	1 year	1 year
Maximum [Member]
Lessee Lease Description [Line Items]
Lessee, operating lease, renewal term	5 years	5 years