Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Tax expense as result of the Tax Act			$ 3,900
Accumulated other comprehensive income, deferred tax (benefit) expense	$ 6,600	$ (2,400)	(1,400)
Accumulated other comprehensive income, a deferred tax expense (benefit)	463	$ (379)	315
Retained earnings amount for which no provision for income tax has been made	51,800
Unrecognized tax liability	13,400
Federal
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards, limitations on use			$ 197
Beacon Trust
Operating Loss Carryforwards [Line Items]
Unused capital loss carryforwards	$ 1,500