Subsequent Event (Unaudited)	12 Months Ended
	Dec. 31, 2021
Subsequent Events [Abstract]
Subsequent Event (Unaudited)	Subsequent Event (Unaudited)1st Constitution BancorpOn January 6, 2022, the Company completed its acquisition of 1st Constitution Bancorp ("1st Constitution"), a bank holding company headquartered in Cranbury, New Jersey. 1st Constitution was the parent of 1st Constitution Bank, which operated 25 branches in Bergen, Mercer, Middlesex, Monmouth, Ocean and Somerset Counties in New Jersey. This acquisition enabled the Company to broaden its presence in those counties. Effective as of the close of business on January 6, 2022, 1st Constitution merged into the Company and 1st Constitution Bank merged into Lakeland. Pursuant to the merger agreement, the shareholders of 1st Constitution received for each outstanding share of 1st Constitution common stock that they owned at the effective time of the merger, 1.3577 shares of Lakeland Bancorp, Inc. common stock. The Company issued 14,020,495 shares of its common stock in the merger. Outstanding 1st Constitution options were paid out in cash at the difference between $25.55 and an average strike price of $15.95 for a total cash payment of $559,000. Given the close proximity between the transaction closing date and the Company’s Annual Report on Form 10-K, the preliminary purchase price allocation has not yet been completed. Management expects to complete the initial accounting for 1st Constitution, including the purchase price allocation, later in the first quarter of 2022. As a result, the estimated fair values of the assets acquired and liabilities assumed, the valuation techniques and inputs used to measure and develop the fair values and any goodwill recorded will be disclosed in the Company’s Quarterly Report on Form 10-Q for the period ended March 31, 2022. Full system integration was completed in February 2022 and three 1st Constitution Bank and one Lakeland Bank branches were closed.