FAIR VALUE MEASUREMENTS (Carrying Values and Estimated Fair Values of the Company's Financial Instruments) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
ASSETS
Cash and cash equivalents	$ 578,053	$ 199,373
Securities available for sale, at fair value	1,558,048	974,222
HTM securities	47,649	203,483
Restricted stock	104,837	75,283
Loans held for sale	40,190	40,662
Net loans	9,149,667	7,117,593
Derivatives:
Cash flow hedges		49
Fair value hedges	2,925	1,598
Best efforts forward delivery commitments		12
Accrued interest receivable	37,314	26,427
Bank owned life insurance	260,124	182,854
LIABILITIES
Deposits	9,814,479	6,977,845
Borrowings	1,287,968	1,198,645
Accrued interest payable	3,794	2,538
Derivatives:
Interest rate swap	20,606	1,350
Cash flow hedges	3,671	8,005
Best efforts forward delivery commitments	182
Fair value hedges	35	76
Interest Rate Swap
Derivatives:
Interest rate derivative	20,606	1,350
Interest Rate Lock Commitments
Derivatives:
Interest rate lock commitments	200	559
Carrying Value
ASSETS
Cash and cash equivalents	578,053	199,373
Securities available for sale, at fair value	1,558,048	974,222
HTM securities	47,604	199,639
Restricted stock	104,837	75,283
Loans held for sale	40,190	40,662
Net loans	9,248,989	7,103,344
Derivatives:
Cash flow hedges		49
Fair value hedges	2,925	1,598
Best efforts forward delivery commitments		12
Accrued interest receivable	37,314	26,427
Bank owned life insurance	260,124	182,854
LIABILITIES
Deposits	9,797,272	6,991,718
Borrowings	1,300,276	1,219,414
Accrued interest payable	3,794	2,538
Derivatives:
Interest rate swap	20,606	1,350
Cash flow hedges	3,671	8,005
Best efforts forward delivery commitments	182
Fair value hedges	35	76
Carrying Value \| Interest Rate Swap
Derivatives:
Interest rate derivative	20,606	1,350
Carrying Value \| Interest Rate Lock Commitments
Derivatives:
Interest rate lock commitments	200	559
Quoted Prices in Active Markets for Identical Assets Level 1
ASSETS
Cash and cash equivalents	578,053	199,373
Securities available for sale, at fair value	0	0
HTM securities	0	0
Restricted stock	0	0
Loans held for sale	0	0
Net loans	0	0
Derivatives:
Cash flow hedges		0
Fair value hedges	0	0
Best efforts forward delivery commitments		0
Accrued interest receivable	0	0
Bank owned life insurance	0	0
LIABILITIES
Deposits	0	0
Borrowings	0	0
Accrued interest payable	0	0
Derivatives:
Interest rate swap	0	0
Cash flow hedges	0	0
Best efforts forward delivery commitments	0
Fair value hedges	0	0
Quoted Prices in Active Markets for Identical Assets Level 1 \| Interest Rate Swap
Derivatives:
Interest rate derivative	0	0
Quoted Prices in Active Markets for Identical Assets Level 1 \| Interest Rate Lock Commitments
Derivatives:
Interest rate lock commitments	0	0
Significant Other Observable Inputs Level 2
ASSETS
Cash and cash equivalents	0	0
Securities available for sale, at fair value	1,558,048	974,222
HTM securities	47,649	203,483
Restricted stock	104,837	75,283
Loans held for sale	40,190	40,662
Net loans	0	0
Derivatives:
Cash flow hedges		49
Fair value hedges	2,925	1,598
Best efforts forward delivery commitments		0
Accrued interest receivable	37,314	26,427
Bank owned life insurance	260,124	182,854
LIABILITIES
Deposits	9,814,479	6,977,845
Borrowings	1,287,968	1,198,645
Accrued interest payable	3,794	2,538
Derivatives:
Interest rate swap	20,606	1,350
Cash flow hedges	3,671	8,005
Best efforts forward delivery commitments	0
Fair value hedges	35	76
Significant Other Observable Inputs Level 2 \| Interest Rate Swap
Derivatives:
Interest rate derivative	20,606	1,350
Significant Other Observable Inputs Level 2 \| Interest Rate Lock Commitments
Derivatives:
Interest rate lock commitments	0	0
Significant Unobservable Inputs Level 3
ASSETS
Cash and cash equivalents	0	0
Securities available for sale, at fair value	0	0
HTM securities	0	0
Restricted stock	0	0
Loans held for sale	0	0
Net loans	9,149,667	7,117,593
Derivatives:
Cash flow hedges		0
Fair value hedges	0	0
Best efforts forward delivery commitments		12
Accrued interest receivable	0	0
Bank owned life insurance	0	0
LIABILITIES
Deposits	0	0
Borrowings	0	0
Accrued interest payable	0	0
Derivatives:
Interest rate swap	0	0
Cash flow hedges	0	0
Best efforts forward delivery commitments	182
Fair value hedges	0	0
Significant Unobservable Inputs Level 3 \| Interest Rate Swap
Derivatives:
Interest rate derivative	0	0
Significant Unobservable Inputs Level 3 \| Interest Rate Lock Commitments
Derivatives:
Interest rate lock commitments	$ 200	$ 559

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