FAIR VALUE (Financial Assets and Liabilities at Dates Indicated that Were Accounted for or Disclosed at Fair Value) (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	$ 1,427,880	$ 1,348,021
Residential mortgage loans held for sale (at fair value)	84,930	78,294
Residential Mortgage Loans Held For Sale
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Residential mortgage loans held for sale (at fair value)		75,500	$ 83,300
U.S. treasuries and government agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	48,086	43,297
State and municipal
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	366,032	390,367
Mortgage-backed and asset-backed
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	1,006,179	904,432
Corporate debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	7,583	9,925
Fair Value, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	1,427,880	1,348,021
Total assets	1,519,212	1,435,498
Total liabilities	(6,402)	(9,183)
Fair Value, Recurring | Residential Mortgage Loans Held For Sale
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Residential mortgage loans held for sale	84,930	78,294
Fair Value, Recurring | U.S. treasuries and government agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	48,086	43,297
Fair Value, Recurring | State and municipal
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	366,032	390,367
Fair Value, Recurring | Mortgage-backed and asset-backed
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	1,006,179	904,432
Fair Value, Recurring | Corporate debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	7,583	9,925
Fair Value, Recurring | Interest rate swap agreements
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swap agreements	6,402	9,183
Interest rate swap agreements	(6,402)	(9,183)
Fair Value, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	0	0
Total assets	0	0
Total liabilities	0	0
Fair Value, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Residential Mortgage Loans Held For Sale
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Residential mortgage loans held for sale	0	0
Fair Value, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. treasuries and government agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	0	0
Fair Value, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | State and municipal
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	0	0
Fair Value, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Mortgage-backed and asset-backed
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	0	0
Fair Value, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	0	0
Fair Value, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest rate swap agreements
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swap agreements	0	0
Interest rate swap agreements	0	0
Fair Value, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	1,420,297	1,338,096
Total assets	1,511,629	1,425,573
Total liabilities	(6,402)	(9,183)
Fair Value, Recurring | Significant Other Observable Inputs (Level 2) | Residential Mortgage Loans Held For Sale
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Residential mortgage loans held for sale	84,930	78,294
Fair Value, Recurring | Significant Other Observable Inputs (Level 2) | U.S. treasuries and government agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	48,086	43,297
Fair Value, Recurring | Significant Other Observable Inputs (Level 2) | State and municipal
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	366,032	390,367
Fair Value, Recurring | Significant Other Observable Inputs (Level 2) | Mortgage-backed and asset-backed
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	1,006,179	904,432
Fair Value, Recurring | Significant Other Observable Inputs (Level 2) | Corporate debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	0	0
Fair Value, Recurring | Significant Other Observable Inputs (Level 2) | Interest rate swap agreements
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swap agreements	6,402	9,183
Interest rate swap agreements	(6,402)	(9,183)
Fair Value, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	7,583	9,925
Total assets	7,583	9,925
Total liabilities	0	0
Fair Value, Recurring | Significant Unobservable Inputs (Level 3) | Residential Mortgage Loans Held For Sale
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Residential mortgage loans held for sale	0	0
Fair Value, Recurring | Significant Unobservable Inputs (Level 3) | U.S. treasuries and government agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	0	0
Fair Value, Recurring | Significant Unobservable Inputs (Level 3) | State and municipal
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	0	0
Fair Value, Recurring | Significant Unobservable Inputs (Level 3) | Mortgage-backed and asset-backed
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	0	0
Fair Value, Recurring | Significant Unobservable Inputs (Level 3) | Corporate debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sales of investment available-for-sale	7,583	9,925
Fair Value, Recurring | Significant Unobservable Inputs (Level 3) | Interest rate swap agreements
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swap agreements	0	0
Interest rate swap agreements	$ 0	$ 0