FAIR VALUE - Summary of Carrying Value and Fair Value of Company's Financial Instruments (Details) - USD ($) $ in Thousands		Sep. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity		$ 374,773	$ 372,498
Loans, net		3,358,759	2,856,136
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity	[1]	0	0
Time deposits with other banks		0
Loans, net		0	0
Deposit liabilities		0	0
Subordinated debt		0	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity	[1]	374,961	369,881
Time deposits with other banks		0
Loans, net		0	0
Deposit liabilities		0	0
Subordinated debt		55,072	54,908
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity	[1]	0	0
Time deposits with other banks		14,557
Loans, net		3,328,023	2,840,993
Deposit liabilities		4,110,324	3,523,322
Subordinated debt		0	0
Carrying Amount [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity	[1]	374,773	372,498
Time deposits with other banks		14,591
Loans, net		3,345,978	2,852,016
Deposit liabilities		4,112,600	3,523,245
Subordinated debt		$ 70,451	$ 70,241

[1] See Note D for further detail of fair value of individual investment categories.