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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LOAN PORTFOLIO - Loan Portfolio Held for Investment (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	$ 9,113,955		$ 8,858,123	$ 8,640,291
Allowance for loan and lease losses	(172,011)	$ (183,732)	(196,362)	(222,035)	$ (225,856)	$ (231,843)
Loans and Leases Receivable, Net Amount	8,941,944		8,661,761
Commercial Portfolio Segment [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	3,930,293		3,750,202
Commercial Portfolio Segment [Member] \| Mortgage Receivable [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	1,550,364		1,522,662	1,533,308
Allowance for loan and lease losses	(46,373)	(53,430)	(55,581)	(48,718)	(50,393)	(48,493)
Commercial Portfolio Segment [Member] \| Commercial And Industrial Sector [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	2,279,685		2,148,111	2,009,049
Allowance for loan and lease losses	(21,644)	(22,321)	(32,546)	(44,000)	(47,659)	(48,871)
Commercial Portfolio Segment [Member] \| Construction Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	100,244		79,429	84,683
Allowance for loan and lease losses	(3,026)	(3,331)	(3,592)	(3,949)	(4,122)	(4,522)
Consumer Portfolio Segment [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	2,112,916		1,944,713	1,775,250
Allowance for loan and lease losses	(52,684)	(52,764)	(53,849)	(70,238)	(67,296)	(70,982)
Consumer Portfolio Segment [Member] \| Consumer Loan [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	1,742,009		1,611,177
Consumer Portfolio Segment [Member] \| Finance Lease [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	370,907		333,536
Residential Portfolio Segment [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross	3,070,746		3,163,208	3,238,001
Allowance for loan and lease losses	$ (48,284)	$ (51,886)	$ (50,794)	$ (55,130)	$ (56,386)	$ (58,975)