Business Combinations - Narrative (Details)		3 Months Ended			9 Months Ended
	Jan. 06, 2022 USD ($) branch lease $ / shares shares	Jun. 30, 2023 USD ($) shares	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($)
Business Acquisition [Line Items]
Assets			$ 10,515,599,000		$ 10,515,599,000		$ 8,198,056,000
Loans			7,499,947,000		7,499,947,000		5,918,101,000
Deposits			8,677,799,000		8,677,799,000		6,965,823,000
Merger-related expenses			3,488,000	$ 1,072,000	8,073,000	$ 1,072,000
Operating lease right-of-use assets			25,854,000		25,854,000		15,222,000
Operating lease liabilities			27,224,000		27,224,000		$ 16,523,000
Provident Financial Services, Inc. (Combined) | Forecast
Business Acquisition [Line Items]
Assets		$ 25,000,000,000
Loans		18,000,000,000
Deposits		$ 20,000,000,000
Provident Financial Services, Inc. (Combined) | Provident Financial Services, Inc. | Forecast
Business Acquisition [Line Items]
Business combination, merger, shareholder interest in combined entity, ownership percentage		58.00%
Provident Financial Services, Inc. (Combined) | Lakeland Shareholders | Forecast
Business Acquisition [Line Items]
Business combination, merger, shareholder interest in combined entity, ownership percentage		42.00%
Lakeland Bancorp, Inc
Business Acquisition [Line Items]
Merger-related expenses			3,500,000		3,500,000
Lakeland Bancorp, Inc | Forecast
Business Acquisition [Line Items]
Business combination, consideration transferred		$ 1,300,000,000
Lakeland Bancorp, Inc | Provident Financial Services, Inc. | Forecast
Business Acquisition [Line Items]
Business combination, consideration transferred, equity interests issued and issuable, entity shares issued per acquiree share (in shares) | shares		0.8319
1st Constitution Bancorp
Business Acquisition [Line Items]
Business combination, consideration transferred, equity interests issued and issuable, entity shares issued per acquiree share (in shares) | shares	1.3577
Merger-related expenses			$ 0	$ 1,100,000	$ 4,600,000	$ 1,100,000
Number of operating bank branches | branch	25
Consideration paid through common stock (in shares) | shares	14,020,495
Business acquisition, share price (in usd per share) | $ / shares	$ 25.55
Business acquisition, average strike price (in usd per share) | $ / shares	$ 15.95
Payments to acquire businesses, gross	$ 559,000
Number of operating bank branches, owned premises | branch	8
Number of lease obligations | lease	17
Operating lease right-of-use assets	$ 13,000,000
Operating lease liabilities	13,000,000
Other intangible assets	$ 9,018,000
Useful life	10 years