Loans and Leases and Other Real Estate - Composition of Lakeland`s Loan and Lease Portfolio (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 4,156,680	$ 3,873,895
Less deferred fees	(3,960)	(3,297)
Loans and leases, net of deferred fees	4,152,720	3,870,598
Commercial, secured by real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	2,831,184	2,556,601
Commercial, industrial and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	340,400	350,228
Leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	75,039	67,016
Real estate - residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	322,880	349,581
Real estate - construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	264,908	211,109
Home equity and consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 322,269	$ 339,360