LOANS AND LEASES - Additional Allowance for Credit Losses Relating to Acquired Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on acquired loans	$ 177,881	$ 176,574	$ 175,380	$ 170,016	$ 165,699	$ 158,059
Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on acquired loans	4,570	$ 3,959	6,698	$ 6,782	$ 6,607	$ 7,268
Acquired Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on acquired loans	2,440		4,976
Acquired Loans [Member] | Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on acquired loans	639		(415)
Acquired Loans [Member] | Total Commercial Loans and Leases [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on acquired loans	3,079		4,561
Acquired Loans [Member] | Direct Installment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on acquired loans	967		1,553
Acquired Loans [Member] | Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on acquired loans	520		484
Acquired Loans [Member] | Indirect Installment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on acquired loans	226		177
Acquired Loans [Member] | Consumer Lines of Credit [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on acquired loans	(222)		(77)
Acquired Loans [Member] | Consumer Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on acquired loans	$ 1,491		$ 2,137