FAIR VALUE (Carrying Amounts and Fair Values of Company's Financial Instruments) (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financial Assets
Other equity securities	$ 45,518	$ 46,094
Loans, net of allowance	4,268,991	3,883,741
Other assets	95,730	93,328
Financial Liabilities
Time Deposits	688,951	586,039
Securities sold under retail repurchase agreements and federal funds purchased	119,359	125,119
Advances from FHLB	765,833	790,000
Subordinated debentures	0	30,000
Estimate of Fair Value Measurement [Member]
Financial Assets
Other equity securities	45,518	46,094
Loans, net of allowance	4,320,719	3,933,700
Other assets	95,730	93,328
Financial Liabilities
Time Deposits	684,139	584,868
Securities sold under retail repurchase agreements and federal funds purchased	119,359	125,119
Advances from FHLB	769,860	800,756
Subordinated debentures	0	29,985
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Assets
Other equity securities	0	0
Loans, net of allowance	0	0
Other assets	0	0
Financial Liabilities
Time Deposits	0	0
Securities sold under retail repurchase agreements and federal funds purchased	0	0
Advances from FHLB	0	0
Subordinated debentures	0	0
Significant Other Observable Inputs (Level 2)
Financial Assets
Other equity securities	45,518	46,094
Loans, net of allowance	0	0
Other assets	95,730	93,328
Financial Liabilities
Time Deposits	684,139	584,868
Securities sold under retail repurchase agreements and federal funds purchased	119,359	125,119
Advances from FHLB	769,860	800,756
Subordinated debentures	0	0
Significant Unobservable Inputs (Level 3)
Financial Assets
Other equity securities	0	0
Loans, net of allowance	4,320,719	3,933,700
Other assets	0	0
Financial Liabilities
Time Deposits	0	0
Securities sold under retail repurchase agreements and federal funds purchased	0	0
Advances from FHLB	0	0
Subordinated debentures	$ 0	$ 29,985