SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Additional Information (Details)	1 Months Ended	3 Months Ended			6 Months Ended
	May 31, 2020 shares	Jun. 30, 2022 USD ($) $ / shares shares	Jun. 30, 2021 USD ($) shares	Sep. 30, 2020 USD ($)	Jun. 30, 2022 USD ($) Segment $ / shares shares	Jun. 30, 2021 USD ($) shares	Jan. 01, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020
Summary Of Significant Accounting Policies [Line Items]
Net decrease to retained earnings		$ (309,899,000)			$ (309,899,000)			$ (274,288,000)
Reduction to allowance for credit losses		(991,000)			$ (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		$ 138,100,000			$ 138,100,000			$ 97,500,000
Threshold period for loan					30 days
Threshold for determining nonaccrual status		90 days			90 days
Non-impaired special mention loans multiple								2.25
Non-impaired substandard loans multiple									3.25
Loan modifications					$ 947,000,000.0
Post-modification outstanding recorded investment			$ 3,139,000		$ 12,471,000	$ 3,139,000
Sale of loans servicing released to third party			$ 56,500,000	$ 355,000,000.0		$ 124,000,000
Closing stock price of common stock | $ / shares		$ 29.70			$ 29.70
Stock options granted | shares		0			0
Issuance of shares for Employee Stock Purchase Plan, shares | shares		7,120	6,347		13,928	14,772
Antidilutive securities | shares		300,925	13,374		300,925	262,423
Restricted stock [Member]
Summary Of Significant Accounting Policies [Line Items]
Shares granted | shares		1,624			235,534
Compensation cost		$ 1,800,000	$ 1,800,000		$ 3,600,000	$ 3,500,000
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			71,482
Restricted Stock Units [Member]
Summary Of Significant Accounting Policies [Line Items]
Unrecognized compensation cost		$ 19,000,000.0			$ 19,000,000.0
Weighted average period over which unrecognized compensation is expected to be recognized (in years)					1 year 5 months 23 days
Employee Stock [Member]
Summary Of Significant Accounting Policies [Line Items]
Compensation cost		$ 42,000	$ 26,000		$ 77,000	$ 56,000
Number of share purchase rights authorized | shares		150,000			150,000
Additional common stock to be issued | shares	200,000
Share purchase rights offering period					12 months
Percentage of closing market price on purchase date					85.00%
Deferral [Member]
Summary Of Significant Accounting Policies [Line Items]
Post-modification outstanding recorded investment					$ 12,656,000
U.S. Small Business Administration (SBA) Loans [Member]
Summary Of Significant Accounting Policies [Line Items]
Paycheck Protection Program, maximum credit facility		$ 650,000,000			650,000,000
Paycheck protection program loans remaining balance		$ 9,400,000			$ 9,400,000
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		$ 15,000,000.0			$ 15,000,000.0			$ 32,500,000
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Cash equivalents original maturities period					90 days
Short term borrowings original maturities period					90 days
Paycheck Protection Loans Repayment Period					5 years
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
Stock option vesting term					5 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]
Paycheck Protection Loans Repayment Period					2 years
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 decrease 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%