Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

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LOAN PORTFOLIO - Loan Portfolio Held for Investment (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	$ 8,858,123	$ 8,850,476	$ 8,886,873
Less: allowance for loan and lease losses	(196,362)	(231,843)	(205,603)	$ (240,710)
Loans held for investment, net	8,661,761	8,618,633
Commercial and Industrial loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	2,148,111	2,083,253
Commercial mortgage loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	1,522,662	1,614,972
Total commercial loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	3,750,202	3,809,622
Total commercial loans [Member] \| Commercial and Industrial loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	2,148,111	2,083,253	2,180,455
Less: allowance for loan and lease losses	(32,546)	(48,871)	(61,953)	(68,768)
Finance leases [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	333,536	257,462
Consumer Portfolio [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	1,944,713	1,749,897	1,716,628
Less: allowance for loan and lease losses	(53,849)	(70,982)	(49,847)	(60,642)
Construction loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	79,429	111,397	124,951
Less: allowance for loan and lease losses	(3,592)	(4,522)	$ (2,562)	$ (3,519)
Construction loans [Member] \| Total commercial loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	47,965	76,556
Residential mortgage loans, mainly secured by first mortgages [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	3,163,208	3,290,957
Consumer Loan [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	1,611,177	1,492,435
Consumer Loan [Member] \| Finance leases [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	1,944,713	1,749,897
Less: allowance for loan and lease losses	$ (53,849)	$ (70,982)