| Document and Entity Information | Apr. 06, 2020 |
| Cover [Abstract] | |
| Entity Registrant Name | LAKELAND BANCORP INC |
| Amendment Flag | false |
| Entity Central Index Key | 0000846901 |
| Current Fiscal Year End Date | --12-31 |
| Document Type | 8-K |
| Document Period End Date | Apr. 6, 2020 |
| 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 |
