Employee Benefit Plans - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2019 USD ($) Installment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2008 USD ($)	Dec. 31, 2003 USD ($)
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	$ 1,300,000	$ 1,100,000	$ 1,000,000.0
Supplemental Employee Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Annual retirement benefit		$ 90,000		$ 84,500			$ 150,000	$ 150,000
Retirement benefit period		10 years		15 years			15 years	15 years
Compensation expense	371,000	$ 83,000	261,000
Retirement age of CEO		65 years		66 years			65 years	65 years
Accrued liabilities	3,400,000	$ 3,300,000
Supplemental Employee Retirement Plan | Somerset Hills Bancorp
Defined Benefit Plan Disclosure [Line Items]
Retirement benefit period						15 years
Employee benefit plan liability	616,000	629,000
Compensation expense	59,000	(1,000)	33,000
Supplemental Employee Retirement Plan | Somerset Hills Bancorp | Chief Financial Officer
Defined Benefit Plan Disclosure [Line Items]
Annual retirement benefit						$ 24,000
Supplemental Employee Retirement Plan | Somerset Hills Bancorp | CEO
Defined Benefit Plan Disclosure [Line Items]
Annual retirement benefit						$ 48,000
Deferred Compensation Agreement
Defined Benefit Plan Disclosure [Line Items]
Expense related to the deferred compensation plan	311,000	269,000	244,000
Accrued liability on deferred compensation plans	$ 1,200,000	923,000
Deferred Compensation Agreement | CEO
Defined Benefit Plan Disclosure [Line Items]
Employer monthly contribution					$ 16,500
Number of consecutive installments payments | Installment	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	$ 136,000	73,000	$ 55,000
Accrued liability on deferred compensation plans	$ 2,000,000.0	$ 1,400,000
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%