Loans and Leases and Other Real Estate - Lakeland 's Commercial Loan Portfolio (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 4,117,265	$ 3,839,353
Commercial, secured by real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,831,184	2,556,601
Commercial, secured by real estate | 1
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Commercial, secured by real estate | 2
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Commercial, secured by real estate | 3
Financing Receivable, Recorded Investment [Line Items]
Total loans	76,824	82,102
Commercial, secured by real estate | 4
Financing Receivable, Recorded Investment [Line Items]
Total loans	862,537	729,281
Commercial, secured by real estate | 5
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,779,908	1,615,331
Commercial, secured by real estate | 5W - Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans	47,178	68,372
Commercial, secured by real estate | 6 - Other assets especially mentioned
Financing Receivable, Recorded Investment [Line Items]
Total loans	40,245	33,015
Commercial, secured by real estate | 7 - Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	24,492	28,500
Commercial, secured by real estate | 8 - Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Commercial, secured by real estate | 9 - Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Total loans	340,400	350,228
Commercial, industrial and other | 1
Financing Receivable, Recorded Investment [Line Items]
Total loans	392	1,449
Commercial, industrial and other | 2
Financing Receivable, Recorded Investment [Line Items]
Total loans	26,968	26,743
Commercial, industrial and other | 3
Financing Receivable, Recorded Investment [Line Items]
Total loans	35,950	36,644
Commercial, industrial and other | 4
Financing Receivable, Recorded Investment [Line Items]
Total loans	96,426	135,702
Commercial, industrial and other | 5
Financing Receivable, Recorded Investment [Line Items]
Total loans	150,928	129,366
Commercial, industrial and other | 5W - Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,779	6,395
Commercial, industrial and other | 6 - Other assets especially mentioned
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,670	5,242
Commercial, industrial and other | 7 - Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,287	8,687
Commercial, industrial and other | 8 - Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Commercial, industrial and other | 9 - Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Real estate - construction
Financing Receivable, Recorded Investment [Line Items]
Total loans	264,908	211,109
Real estate - construction | 1
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Real estate - construction | 2
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Real estate - construction | 3
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Real estate - construction | 4
Financing Receivable, Recorded Investment [Line Items]
Total loans	15,502	28,177
Real estate - construction | 5
Financing Receivable, Recorded Investment [Line Items]
Total loans	246,806	175,595
Real estate - construction | 5W - Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	1,223
Real estate - construction | 6 - Other assets especially mentioned
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Real estate - construction | 7 - Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,600	6,114
Real estate - construction | 8 - Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Real estate - construction | 9 - Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 0	$ 0