| Document and Entity Information | Jan. 28, 2021 |
| Cover [Abstract] | |
| Entity Registrant Name | BCB BANCORP INC |
| Amendment Flag | false |
| Entity Central Index Key | 0001228454 |
| Document Type | 8-K |
| Document Period End Date | Jan. 28, 2021 |
| Entity Incorporation State Country Code | NJ |
| Entity File Number | 0-50275 |
| Entity Tax Identification Number | 26-0065262 |
| Entity Address, Address Line One | 104-110 Avenue C |
| Entity Address, City or Town | Bayonne |
| Entity Address, State or Province | NJ |
| Entity Address, Postal Zip Code | 07002 |
| City Area Code | (201) |
| Local Phone Number | 823-0700 |
| 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 | BCBP |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
