SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Additional Information (Details)	1 Months Ended	3 Months Ended
	May 31, 2020 shares	Mar. 31, 2023 USD ($) Segment $ / shares shares	Mar. 31, 2022 USD ($) shares	Dec. 31, 2022 USD ($)	Jan. 01, 2022 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Net increase to retained earnings		$ 366,270,000		$ 348,798,000
Reduction to allowance for credit losses		$ (801,000)	$ (188,000)	(752,000)
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		$ 158,600,000		152,200,000
Threshold period for loan		30 days
Threshold for determining nonaccrual status		90 days
Post-modification outstanding recorded investment			$ 12,500,000
Closing stock price of common stock | $ / shares		$ 29.62
Stock options granted | shares		0
Unrecognized compensation cost		$ 0
Issuance of shares for Employee Stock Purchase Plan, shares | shares		7,533	6,808
Antidilutive securities | shares		362,052	299,433
Goodwill impairment		$ 0
Restricted stock [Member]
Summary Of Significant Accounting Policies [Line Items]
Shares granted | shares		269,570
Compensation cost		$ 2,700,000	$ 1,900,000
Restricted stock [Member] | Tranche One [Member]
Summary Of Significant Accounting Policies [Line Items]
Stock option vesting term		3 years
Restricted stock [Member] | Tranche Two [Member]
Summary Of Significant Accounting Policies [Line Items]
Stock option vesting term		5 years
Performance Shares [Member]
Summary Of Significant Accounting Policies [Line Items]
Shares granted | shares		123,137
Restricted Stock Units [Member]
Summary Of Significant Accounting Policies [Line Items]
Unrecognized compensation cost		$ 23,000,000.0
Weighted average period over which unrecognized compensation is expected to be recognized (in years)		1 year 5 months 8 days
Employee Stock [Member]
Summary Of Significant Accounting Policies [Line Items]
Compensation cost		$ 48,000	$ 35,000
Number of share purchase rights authorized | shares		150,000
Additional common stock to be issued | shares	200,000
Percentage of closing market price on purchase date		85.00%
Consumer and Other [Member] | Closed-end Loans [Member]
Summary Of Significant Accounting Policies [Line Items]
Threshold for determining nonaccrual status		120 days
Consumer and Other [Member] | Open-end Loans [Member]
Summary Of Significant Accounting Policies [Line Items]
Threshold for determining nonaccrual status		180 days
Small Business Administration Loans [Member]
Summary Of Significant Accounting Policies [Line Items]
Loans held for sale		$ 15,100,000		$ 17,200,000
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Cash equivalents original maturities period		90 days
Short term borrowings 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%
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%
ASU 2016-13 [Member]
Summary Of Significant Accounting Policies [Line Items]
Net increase to retained earnings					$ 3,900,000
Reduction to allowance for credit losses					$ 5,500,000
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%