FAIR VALUE - Summary of Carrying Value and Fair Value of Company's Financial Instruments (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity		$ 416,863	$ 372,498
Loans, net		3,790,255	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		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]	414,472	369,881
Time deposits with other banks		0
Loans, net		0	0
Deposit		0	0
Subordinated debt		61,530	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		12,493
Loans, net		3,760,754	2,840,993
Deposit		4,588,515	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]	416,863	372,498
Time deposits with other banks		12,553
Loans, net		3,786,063	2,852,016
Deposit		4,592,720	3,523,245
Subordinated debt		$ 70,521	$ 70,241

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