FAIR VALUE MEASUREMENTS - CARRYING AMOUNTS AND ESTIMATED FAIR VALUE OF FINANCIAL ASSETS AND LIBILITIES (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015		Sep. 30, 2015	Dec. 31, 2014
Financial assets:
Cash and cash equivalents	$ 162,278	$ 111,918		$ 77,755	$ 132,365
Investment securities	965,960	689,132	[1]
Investment securities held to maturity	38,847	39,182	[1]
Loans held for sale	85,964	47,287	[1]
Loans, net	5,241,167	3,066,775	[1]
Purchased accounts receivable	7,907	52,688	[1]
Federal Home Loan Bank stock	41,693	24,844	[1]
Derivative assets	1,819	996
Accrued interest receivable	19,519	12,695
Financial liabilities:
Deposits	5,310,028	3,310,297	[1]
Short-term borrowings	791,721	375,500	[1]
Long-term debt	164,215	194,967	[1]
Derivative liabilities	10,829	4,376
Accrued interest payable	2,438	2,550
Level 1
Financial assets:
Cash and cash equivalents, Fair Value	162,278	111,918
Investment securities	32,320	16,532
Investment securities held to maturity, fair value	0	0
Loans held for sale, Fair Value	0	0
Loans held for investment, Fair Value	0	0
Purchased accounts receivable	0	0
Federal Home Loan Bank stock, at cost	0	0
Derivative assets	0	0
Accrued interest receivable, Fair Value	0	0
Financial liabilities:
Deposits, Fair Value	0	0
Short term borrowings, Fair Value	0	0
Long-term debt, Fair Value	0	0
Derivative liabilities, Fair Value	0	0
Accrued interest payable, Fair Value	0	0
Level 2
Financial assets:
Cash and cash equivalents, Fair Value	0	0
Investment securities	922,003	665,872
Investment securities held to maturity, fair value	40,681	40,500
Loans held for sale, Fair Value	85,964	47,287
Loans held for investment, Fair Value	35,030	23,664
Purchased accounts receivable	7,907	52,688
Federal Home Loan Bank stock, at cost	41,693	24,844
Derivative assets	625	588
Accrued interest receivable, Fair Value	19,519	12,695
Financial liabilities:
Deposits, Fair Value	5,313,683	3,310,306
Short term borrowings, Fair Value	0	0
Long-term debt, Fair Value	0	0
Derivative liabilities, Fair Value	10,829	4,376
Accrued interest payable, Fair Value	2,438	2,550
Level 3
Financial assets:
Cash and cash equivalents, Fair Value	0	0
Investment securities	11,637	6,728
Investment securities held to maturity, fair value	0	0
Loans held for sale, Fair Value	0	0
Loans held for investment, Fair Value	5,262,021	3,068,797
Purchased accounts receivable	0	0
Federal Home Loan Bank stock, at cost	0	0
Derivative assets	1,194	408
Accrued interest receivable, Fair Value	0	0
Financial liabilities:
Deposits, Fair Value	0	0
Short term borrowings, Fair Value	791,721	375,500
Long-term debt, Fair Value	174,426	198,928
Derivative liabilities, Fair Value	0	0
Accrued interest payable, Fair Value	0	0
Estimate of Fair Value Measurement
Financial assets:
Cash and cash equivalents, Fair Value	162,278	111,918
Investment securities	965,960	689,132
Investment securities held to maturity, fair value	40,681	40,500
Loans held for sale, Fair Value	85,964	47,287
Loans held for investment, Fair Value	5,297,051	3,092,461
Purchased accounts receivable	7,907	52,688
Federal Home Loan Bank stock, at cost	41,693	24,844
Derivative assets	1,819	996
Accrued interest receivable, Fair Value	19,519	12,695
Financial liabilities:
Deposits, Fair Value	5,313,683	3,310,306
Short term borrowings, Fair Value	791,721	375,500
Long-term debt, Fair Value	174,426	198,928
Derivative liabilities, Fair Value	10,829	4,376
Accrued interest payable, Fair Value	$ 2,438	$ 2,550

[1] Derived from the audited consolidated financial statements included in the Company's 2015 Annual Report on Form 10-K.