Fair Value Measurement and Fair Value of Financial Instruments - Carrying Values and Fair Values of Company's Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Financial Assets:
Investment securities held to maturity, carrying value	$ 836,377	$ 923,308
Investment securities held to maturity, fair value	702,563	760,455
Federal Home Loan Bank and other membership stock, at cost	52,517	42,483
Federal Home Loan Bank and other membership bank stocks, Fair Value	52,517	42,483
Loans, net, Carrying Value	8,266,698	7,795,786
Loans, net, Fair Value	7,714,736	7,561,997
Financial Liabilities:
Certificates of deposit, Carrying Value	1,967,448	1,208,177
Certificates of deposit, Fair Value	1,953,446	1,174,230
Long-Term Federal Home Loan Bank Advances	325,000	25,000
Federal Home Loan Bank Borrowings, Fair Value Disclosure	333,878	23,001
Subordinate debentures, Carrying Value	194,705	194,264
Subordinated debentures, Fair Value	149,063	160,933
U.S. Treasury and U.S. government agencies
Financial Assets:
Investment securities held to maturity, carrying value	10,406	11,099
Investment securities held to maturity, fair value	9,914	10,385
Mortgage-backed securities, residential
Financial Assets:
Investment securities held to maturity, carrying value	332,509	360,683
Investment securities held to maturity, fair value	280,426	302,612
Collateralized mortgage obligations, residential
Financial Assets:
Investment securities held to maturity, carrying value	12,243	13,026
Investment securities held to maturity, fair value	9,447	10,456
Mortgage-backed securities, multifamily
Financial Assets:
Investment securities held to maturity, carrying value	4,145	5,094
Investment securities held to maturity, fair value	3,494	4,347
Obligations of states and political subdivisions
Financial Assets:
Investment securities held to maturity, carrying value	474,195	530,506
Investment securities held to maturity, fair value	396,859	430,108
Corporate debt securities
Financial Assets:
Investment securities held to maturity, carrying value	2,879	2,900
Investment securities held to maturity, fair value	2,423	2,547
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Assets:
Investment securities held to maturity, fair value	0	0
Federal Home Loan Bank and other membership bank stocks, Fair Value	0	0
Loans, net, Fair Value	0	0
Financial Liabilities:
Certificates of deposit, Fair Value	0	0
Federal Home Loan Bank Borrowings, Fair Value Disclosure	0	0
Subordinated debentures, Fair Value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| U.S. Treasury and U.S. government agencies
Financial Assets:
Investment securities held to maturity, fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Mortgage-backed securities, residential
Financial Assets:
Investment securities held to maturity, fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Collateralized mortgage obligations, residential
Financial Assets:
Investment securities held to maturity, fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Mortgage-backed securities, multifamily
Financial Assets:
Investment securities held to maturity, fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Obligations of states and political subdivisions
Financial Assets:
Investment securities held to maturity, fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Corporate debt securities
Financial Assets:
Investment securities held to maturity, fair value	0	0
Significant Other Observable Inputs (Level 2)
Financial Assets:
Investment securities held to maturity, fair value	702,563	758,982
Federal Home Loan Bank and other membership bank stocks, Fair Value	52,517	42,483
Loans, net, Fair Value	0	0
Financial Liabilities:
Certificates of deposit, Fair Value	1,953,446	1,174,230
Federal Home Loan Bank Borrowings, Fair Value Disclosure	333,878	23,001
Subordinated debentures, Fair Value	0	0
Significant Other Observable Inputs (Level 2) \| U.S. Treasury and U.S. government agencies
Financial Assets:
Investment securities held to maturity, fair value	9,914	10,385
Significant Other Observable Inputs (Level 2) \| Mortgage-backed securities, residential
Financial Assets:
Investment securities held to maturity, fair value	280,426	302,612
Significant Other Observable Inputs (Level 2) \| Collateralized mortgage obligations, residential
Financial Assets:
Investment securities held to maturity, fair value	9,447	10,456
Significant Other Observable Inputs (Level 2) \| Mortgage-backed securities, multifamily
Financial Assets:
Investment securities held to maturity, fair value	3,494	4,347
Significant Other Observable Inputs (Level 2) \| Obligations of states and political subdivisions
Financial Assets:
Investment securities held to maturity, fair value	396,859	428,635
Significant Other Observable Inputs (Level 2) \| Corporate debt securities
Financial Assets:
Investment securities held to maturity, fair value	2,423	2,547
Significant Unobservable Inputs (Level 3)
Financial Assets:
Investment securities held to maturity, fair value	0	1,473
Federal Home Loan Bank and other membership bank stocks, Fair Value	0	0
Loans, net, Fair Value	7,714,736	7,561,997
Financial Liabilities:
Certificates of deposit, Fair Value	0	0
Federal Home Loan Bank Borrowings, Fair Value Disclosure	0	0
Subordinated debentures, Fair Value	149,063	160,933
Significant Unobservable Inputs (Level 3) \| U.S. Treasury and U.S. government agencies
Financial Assets:
Investment securities held to maturity, fair value	0	0
Significant Unobservable Inputs (Level 3) \| Mortgage-backed securities, residential
Financial Assets:
Investment securities held to maturity, fair value	0	0
Significant Unobservable Inputs (Level 3) \| Collateralized mortgage obligations, residential
Financial Assets:
Investment securities held to maturity, fair value	0	0
Significant Unobservable Inputs (Level 3) \| Mortgage-backed securities, multifamily
Financial Assets:
Investment securities held to maturity, fair value	0	0
Significant Unobservable Inputs (Level 3) \| Obligations of states and political subdivisions
Financial Assets:
Investment securities held to maturity, fair value	0	1,473
Significant Unobservable Inputs (Level 3) \| Corporate debt securities
Financial Assets:
Investment securities held to maturity, fair value	$ 0	$ 0

LAKELAND BANCORP INC 10-K