FAIR VALUES OF FINANCIAL INSTRUMENTS - Carrying Amounts and Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Financial assets
Cash and cash equivalents	$ 372,603	$ 156,124
Time deposits in financial institutions	1,500	1,500
Securities available-for-sale	1,941,588	833,596
Securities held-to-maturity	996,319	932,285
Federal Home Loan Bank and other bank stock	69,190	59,069
Loans held-for-sale	856,593	672,850
Loans and leases receivable, net of ALLL	6,667,573	5,244,251
Accrued interest receivable	32,016	22,800
Derivative assets	15,746	9,042
Financial liabilities
Deposits	8,967,692	6,010,606
Advances from Federal Home Loan Bank	770,671	929,727
Other borrowings	50,000
Long term debt	186,079	264,269
Derivative liabilities	4,650	1,067
Accrued interest payable	5,502	4,234
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets
Cash and cash equivalents	372,603	156,124
Time deposits in financial institutions	1,500	1,500
Securities available-for-sale	0	0
Securities held-to-maturity	0	0
Federal Home Loan Bank and other bank stock	0	0
Loans held-for-sale	0	0
Loans and leases receivable, net of ALLL	0	0
Accrued interest receivable	32,016	22,800
Derivative assets	0	0
Financial liabilities
Deposits	0	0
Advances from Federal Home Loan Bank	0	0
Other borrowings	0
Long term debt	0	0
Derivative liabilities	0	0
Accrued interest payable	5,502	4,234
Significant Other Observable Inputs (Level 2)
Financial assets
Cash and cash equivalents	0	0
Time deposits in financial institutions	0	0
Securities available-for-sale	1,941,588	833,596
Securities held-to-maturity	996,319	932,285
Federal Home Loan Bank and other bank stock	69,190	59,069
Loans held-for-sale	808,945	654,559
Loans and leases receivable, net of ALLL	0	0
Accrued interest receivable	0	0
Derivative assets	15,746	9,042
Financial liabilities
Deposits	0	0
Advances from Federal Home Loan Bank	770,671	929,727
Other borrowings	50,000
Long term debt	186,079	264,269
Derivative liabilities	4,650	1,067
Accrued interest payable	0	0
Significant Unobservable Inputs (Level 3)
Financial assets
Cash and cash equivalents	0	0
Time deposits in financial institutions	0	0
Securities available-for-sale	0	0
Securities held-to-maturity	0	0
Federal Home Loan Bank and other bank stock	0	0
Loans held-for-sale	47,648	18,291
Loans and leases receivable, net of ALLL	6,667,573	5,244,251
Accrued interest receivable	0	0
Derivative assets	0	0
Financial liabilities
Deposits	8,967,692	6,010,606
Advances from Federal Home Loan Bank	0	0
Other borrowings	0
Long term debt	0	0
Derivative liabilities	0	0
Accrued interest payable	0	0
Carrying Value
Financial assets
Cash and cash equivalents	372,603	156,124
Time deposits in financial institutions	1,500	1,500
Securities available-for-sale	1,941,588	833,596
Securities held-to-maturity	962,315	962,203
Federal Home Loan Bank and other bank stock	69,190	59,069
Loans held-for-sale	846,844	668,841
Loans and leases receivable, net of ALLL	6,528,558	5,148,861
Accrued interest receivable	32,016	22,800
Derivative assets	15,746	9,042
Financial liabilities
Deposits	9,078,319	6,303,085
Advances from Federal Home Loan Bank	770,000	930,000
Other borrowings	49,903
Long term debt	176,579	261,876
Derivative liabilities	4,650	1,067
Accrued interest payable	$ 5,502	$ 4,234