SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Additional Information (Details)	1 Months Ended	3 Months Ended		9 Months Ended
	May 31, 2020 shares	Sep. 30, 2023 USD ($) $ / shares shares	Sep. 30, 2022 USD ($) shares	Sep. 30, 2023 USD ($) Segment $ / shares shares	Sep. 30, 2022 USD ($) shares	Jun. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)	Jun. 30, 2022 USD ($)	Jan. 01, 2022 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Net increase to retained earnings		$ 386,387,000		$ 386,387,000			$ 348,798,000
Reduction to allowance for credit losses		(743,000)	$ (925,000)	$ (743,000)	$ (925,000)	$ (831,000)	(752,000)	$ (991,000)
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		$ 166,800,000		$ 166,800,000			152,200,000
Threshold period for loan				30 days
Threshold for determining nonaccrual status		90 days		90 days
Post-modification outstanding recorded investment					$ 12,429,000
Closing stock price of common stock | $ / shares		$ 25.65		$ 25.65
Stock options granted | shares		0		0
Unrecognized compensation cost		$ 0		$ 0
Issuance of shares for Employee Stock Purchase Plan, shares | shares		8,850	6,441	26,491	20,369
Antidilutive securities | shares		235,902	112,241	416,712	296,687
Restricted stock [Member]
Summary Of Significant Accounting Policies [Line Items]
Shares granted | shares		0		271,387
Compensation cost		$ 2,300,000	$ 2,100,000	$ 8,600,000	$ 5,700,000
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		0		126,821
Restricted Stock Units [Member]
Summary Of Significant Accounting Policies [Line Items]
Unrecognized compensation cost		$ 17,200,000		$ 17,200,000
Weighted average period over which unrecognized compensation is expected to be recognized (in years)				1 year 3 months 3 days
Employee Stock [Member]
Summary Of Significant Accounting Policies [Line Items]
Compensation cost		$ 34,000	$ 37,000	$ 140,000	$ 114,000
Number of share purchase rights authorized | shares		150,000		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		120 days
Consumer and Other [Member] | Open-end Loans [Member]
Summary Of Significant Accounting Policies [Line Items]
Threshold for determining nonaccrual status		180 days		180 days
Small Business Administration Loans [Member]
Summary Of Significant Accounting Policies [Line Items]
Loans held for sale		$ 7,200,000		$ 7,200,000			$ 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		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		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%		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%		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%		1.00%
Peapack Ventures, LLC [Member] | Peapack-Gladstone Realty, Inc [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of interest owned		21.00%		21.00%