Employee Benefit Plans - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2020 USD ($) installments	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) age	Dec. 31, 2016 USD ($) age	Dec. 31, 2015 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2008 USD ($) age	Dec. 31, 2003 USD ($) age
Defined Benefit Plan Disclosure [Line Items]
Percent of match	50.00%
Employer matching contribution, percent of employees' gross pay	6.00%
Company's contributions to employees salary	$ 1,500,000	$ 1,300,000	$ 1,100,000
Supplemental Employee Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Annual retirement benefit				$ 84,500				$ 150,000
Retirement benefit period				15 years				15 years
Retirement age of CEO | age				66				65
Compensation expense	364,000	371,000	$ 83,000
Accrued liabilities	3,500,000	3,400,000
Supplemental Employee Retirement Plan | CEO
Defined Benefit Plan Disclosure [Line Items]
Annual retirement benefit							$ 150,000
Retirement benefit period							15 years
Retirement age of CEO | age							65
Supplemental Employee Retirement Plan | Former Regional President
Defined Benefit Plan Disclosure [Line Items]
Annual retirement benefit							$ 90,000
Retirement benefit period			10 years
Retirement age of CEO | age			65
Supplemental Employee Retirement Plan | Somerset Hills Bancorp
Defined Benefit Plan Disclosure [Line Items]
Retirement benefit period						15 years
Compensation expense	47,000	59,000	$ (1,000)
Employee benefit plan liability	591,000	616,000
Supplemental Employee Retirement Plan | Somerset Hills Bancorp | CEO
Defined Benefit Plan Disclosure [Line Items]
Annual retirement benefit						$ 48,000
Supplemental Employee Retirement Plan | Somerset Hills Bancorp | CFO
Defined Benefit Plan Disclosure [Line Items]
Annual retirement benefit						$ 24,000
Deferred Compensation Agreement
Defined Benefit Plan Disclosure [Line Items]
Expense related to the deferred compensation plan	339,000	311,000	269,000
Accrued liability on deferred compensation plans	$ 1,600,000	1,200,000
Deferred Compensation Agreement | CEO
Defined Benefit Plan Disclosure [Line Items]
Employer monthly contribution					$ 16,500
Number of consecutive installments payments | installments	180
Deferred Compensation Agreement | Minimum | CEO
Defined Benefit Plan Disclosure [Line Items]
Range of return on equity					0.00%
Deferred Compensation Agreement | Maximum | CEO
Defined Benefit Plan Disclosure [Line Items]
Range of return on equity					15.00%
Elective Deferral Plan
Defined Benefit Plan Disclosure [Line Items]
Expense related to the deferred compensation plan	$ 162,000	136,000	$ 73,000
Accrued liability on deferred compensation plans	$ 2,600,000	$ 2,000,000.0
Elective Deferral Plan | Eligible Executives
Defined Benefit Plan Disclosure [Line Items]
Deferral account, interest rate					75.00%
Elective Deferral Plan | Minimum | Eligible Executives
Defined Benefit Plan Disclosure [Line Items]
Range of return on equity					0.00%
Elective Deferral Plan | Maximum | Eligible Executives
Defined Benefit Plan Disclosure [Line Items]
Range of return on equity					15.00%