Employee Benefit Plans - Additional Information (Detail)	1 Months Ended			12 Months Ended
	Mar. 31, 2015	Feb. 28, 2015 USD ($)	Nov. 30, 2008 USD ($)	Dec. 31, 2017 USD ($) Installments	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2008 USD ($)	Dec. 31, 2003 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Company's contributions to employees salary				$ 1,044,000	$ 911,000	$ 760,000
Employees contributions to their annual salary				50.00%
Percent of match				6.00%
Profit Sharing Plan
Defined Benefit Plan Disclosure [Line Items]
Company's contributions to employees salary				$ 0	600,000	600,000
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				261,000	746,000	$ 814,000
Accrued liabilities				3,500,000	3,500,000
Retirement age of CEO			65 years			66 years		65 years	65 years
Supplemental Employee Retirement Plan | Somerset Hills Bancorp
Defined Benefit Plan Disclosure [Line Items]
Retirement benefit period							15 years
Employee benefit plan liability				702,000	717,000
Compensation expense				33,000	0	$ 95,000
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 | Chief Financial Officer
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				244,000	222,000	188,000,000
Accrued liability on deferred compensation plans				$ 654,000	410,000
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				$ 55,000	22,000	$ 3,000,000
Accrued liability on deferred compensation plans				$ 916,000	$ 512,000
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%