SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Additional Information (Details)		12 Months Ended
	Jan. 01, 2019 USD ($)	Dec. 31, 2019 USD ($) segment Lease branchlocation shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments | segment		2
Federal funds sales periods		1 day
Interest-earning deposits maturities period		1 year
Servicing rights		$ 0
Amount of loans serviced		$ 51,900,000	$ 35,100,000
Threshold period for loan		30 days
Threshold for determining nonaccrual status		90 days
Number of existing finance leases | Lease		2
Number of branch location | branchlocation		1
Issuance of shares for Employee Stock Purchase Plan, shares | shares		18,740	29,273	25,404
Antidilutive securities | shares		277,677	257,422
Dilutive securities | shares				0
Stock dividends excess threshold percentage		20.00%
Stock dividend threshold or less percentage		20.00%
Lease liability	$ 8,200,000	$ 12,423,000
Right-of-use asset	7,900,000	$ 12,132,000
Cumulative effect adjustment to retained earnings	$ 661,000
Employee Stock Option [Member]
Summary Of Significant Accounting Policies [Line Items]
Option term		10 years
Compensation cost		$ 0	$ 0	$ 6,000
Employee Stock [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of share purchase rights authorized | shares		150,000
Share purchase rights offering period		12 months
Percentage of closing market price on purchase date		85.00%
Compensation cost		$ 158,000	$ 189,000	$ 116,000
Premises [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful life		40 years
Substandard [Member]
Summary Of Significant Accounting Policies [Line Items]
Loan reserve multiple		3.5	3.5
Special Mention [Member]
Summary Of Significant Accounting Policies [Line Items]
Loan reserve multiple		2.25	2.25
Consumer and Other [Member]
Summary Of Significant Accounting Policies [Line Items]
Threshold for determining nonaccrual status		120 days
Small Business Administration Loans [Member]
Summary Of Significant Accounting Policies [Line Items]
Loans held for sale		$ 4,600,000	$ 1,200,000
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Cash equivalents original maturities period		90 days
Finite-lived intangible asset, useful life		15 years
Maximum [Member] | Employee Stock Option [Member]
Summary Of Significant Accounting Policies [Line Items]
Option term		10 years
Maximum [Member] | Employee Stock [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of compensation contributable		15.00%
Maximum [Member] | Equipment and Other Fixed Assets [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful life		10 years
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Finite-lived intangible asset, useful life		5 years
Minimum [Member] | Employee Stock [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of compensation contributable		1.00%
Minimum [Member] | Equipment and Other Fixed Assets [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful life		3 years
Peapack-Gladstone Mortgage Group, Inc. [Member] | Peapack Ventures, LLC [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of interest owned		99.00%
Peapack-Gladstone Mortgage Group, Inc. [Member] | Peapack-Gladstone Realty, Inc [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of interest owned		79.00%
PGB Trust & Investments of Delaware [Member] | Peapack Ventures, LLC [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of interest owned		1.00%
Peapack Ventures, LLC [Member] | Peapack-Gladstone Realty, Inc [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of interest owned		21.00%