Goodwill and Other Intangibles - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) Acquisition	Dec. 31, 2018 USD ($)
Finite Lived Intangible Assets [Line Items]
Amortization expense	$ 6,517	$ 5,506	$ 5,764
Corporate Trust Business [Member]
Finite Lived Intangible Assets [Line Items]
Number of business acquired | Acquisition		2
Corporate Trust Business One [Member]
Finite Lived Intangible Assets [Line Items]
Post-closing purchase adjustment	$ 24
Customer Relationship [Member] | Corporate Trust Business [Member]
Finite Lived Intangible Assets [Line Items]
Aggregate intangibles acquired		$ 18,100