LOANS AND LEASES - Additional Allowance for Credit Losses Relating to Acquired Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on acquired loans	$ 170,016	$ 165,699	$ 158,059	$ 156,894	$ 154,369	$ 142,012
Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on acquired loans	6,782	$ 6,607	7,268	$ 6,381	$ 5,650	$ 6,727
Acquired Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on acquired loans	4,242		4,538
Acquired Loans [Member] | Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on acquired loans	0		500
Acquired Loans [Member] | Total Commercial Loans and Leases [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on acquired loans	4,242		5,038
Acquired Loans [Member] | Direct Installment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on acquired loans	1,637		1,005
Acquired Loans [Member] | Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on acquired loans	647		632
Acquired Loans [Member] | Indirect Installment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on acquired loans	213		221
Acquired Loans [Member] | Consumer Lines of Credit [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on acquired loans	$ 43		$ 372