Document and Entity Information
| Document and Entity Information | Jan. 06, 2022 |
| Cover [Abstract] | |
| Entity Registrant Name | LAKELAND BANCORP INC |
| Amendment Flag | true |
| Entity Central Index Key | 0000846901 |
| Document Type | 8-K/A |
| Document Period End Date | Jan. 6, 2022 |
| Entity Incorporation State Country Code | NJ |
| Entity File Number | 000-17820 |
| Entity Tax Identification Number | 22-2953275 |
| Entity Address, Address Line One | 250 Oak Ridge Road |
| Entity Address, City or Town | Oak Ridge |
| Entity Address, State or Province | NJ |
| Entity Address, Postal Zip Code | 07438 |
| City Area Code | (973) |
| Local Phone Number | 697-2000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, no Par Value |
| Trading Symbol | LBAI |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Amendment Description | On January 6, 2022, Lakeland Bancorp, Inc. (“Lakeland”), completed its merger (the “Merger”) with 1st Constitution Bancorp, a New Jersey corporation (“1st Constitution”), pursuant to the Agreement and Plan of Merger, dated as of July 11, 2021, by and between Lakeland and 1st Constitution. At the January 6, 2022 effective time of the Merger (the “Effective Time”), 1st Constitution merged with and into Lakeland, with Lakeland as the resulting corporation. Immediately following the Merger, 1st Constitution Bank, a New Jersey-chartered commercial bank and wholly-owned subsidiary of 1st Constitution, merged with and into Lakeland Bank, a New Jersey-chartered commercial bank and wholly-owned subsidiary of Lakeland, with Lakeland Bank being the surviving bank. |