CREDIT QUALITY ASSESSMENT (Information by Credit Risk Rating Indicators for Those Remaining Segments of Loan Portfolio) (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	$ 6,388,959	$ 4,314,248
Consumer
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	523,011	455,829
Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	1,181,427	921,435
Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	188,779	176,687
Homogeneous Loan Pools
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	1,893,217	1,553,951
Homogeneous Loan Pools | Consumer
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	523,011	455,829
Homogeneous Loan Pools | Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	1,181,427	921,435
Homogeneous Loan Pools | Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	188,779	176,687
Homogeneous Loan Pools | Performing Financing Receivable
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	1,877,806	1,542,496
Homogeneous Loan Pools | Performing Financing Receivable | Consumer
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	518,350	452,862
Homogeneous Loan Pools | Performing Financing Receivable | Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	1,170,840	913,124
Homogeneous Loan Pools | Performing Financing Receivable | Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	188,616	176,510
Homogeneous Loan Pools | Nonperforming Financing Receivable | Loans 90 Days Or More Past Due
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	563	225
Homogeneous Loan Pools | Nonperforming Financing Receivable | Non Accrual Loans
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	13,395	10,340
Homogeneous Loan Pools | Nonperforming Financing Receivable | Restructured Loans
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	1,453	890
Homogeneous Loan Pools | Nonperforming Financing Receivable | Consumer | Loans 90 Days Or More Past Due
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	563	0
Homogeneous Loan Pools | Nonperforming Financing Receivable | Consumer | Non Accrual Loans
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	4,098	2,967
Homogeneous Loan Pools | Nonperforming Financing Receivable | Consumer | Restructured Loans
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	0	0
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Residential Mortgage | Loans 90 Days Or More Past Due
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	0	225
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Residential Mortgage | Non Accrual Loans
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	9,134	7,196
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Residential Mortgage | Restructured Loans
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	1,453	890
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Residential Construction | Loans 90 Days Or More Past Due
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	0	0
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Residential Construction | Non Accrual Loans
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	163	177
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Residential Construction | Restructured Loans
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	$ 0	$ 0