Reserve for loans impairments recorded after acquisition as a result of current information and events which result in it being probable that estimated cash flows will be less than previously expected or because actual cash flows are less than cash flows previously expected. This relates to loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that was acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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ALLOWANCE FOR LOAN AND LEASE LOSSES - Carrying Amount of Portfolios (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable Allowance For Credit Losses [Line Items]
Impaired Financing Receivable With No Related Allowance Recorded Investment	$ 228,906		$ 213,046
Impaired Financing Receivable With Related Allowance Recorded Investment	559,104		577,262
Impaired Financing Receivable Related Allowance	53,313	$ 49,514	51,410	$ 48,155	$ 40,794	$ 64,421
Loans And Leases Receivable Gross Carrying Amount	8,716,953		8,850,476	8,877,214
Loans and Leases Receivable, Allowance	200,563	222,035	231,843	230,870	173,485	205,603
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Allowance For Loan Losses	11,354	11,354	11,251	10,235	9,446	6,857
PCI loans
Financing Receivable Allowance For Credit Losses [Line Items]
Loans And Leases Receivable Gross Carrying Amount	149,122		158,174	157,794
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Allowance For Loan Losses	11,354		11,251	10,235
General Allowance [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans And Leases Receivable Gross Carrying Amount	7,779,821		7,901,994	7,940,161
Loans and Leases Receivable, Allowance	135,896		169,182	172,480
Construction Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Impaired Financing Receivable With No Related Allowance Recorded Investment	1,116		48
Impaired Financing Receivable With Related Allowance Recorded Investment	5,781		47,218
Impaired Financing Receivable Related Allowance	906		2,017	1,865
Loans And Leases Receivable Gross Carrying Amount	82,862		111,397	129,460
Loans and Leases Receivable, Allowance	3,079	3,949	4,522	3,947	3,736	2,562
Construction Loans [Member] \| PCI loans
Financing Receivable Allowance For Credit Losses [Line Items]
Loans And Leases Receivable Gross Carrying Amount	0		0	0
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Allowance For Loan Losses	0		0	0
Construction Loans [Member] \| General Allowance [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans And Leases Receivable Gross Carrying Amount	75,965		64,131	79,087
Loans and Leases Receivable, Allowance	2,173		2,505	2,082
Residential Mortgage Loans
Financing Receivable Allowance For Credit Losses [Line Items]
Impaired Financing Receivable With No Related Allowance Recorded Investment	117,375		116,818
Impaired Financing Receivable With Related Allowance Recorded Investment	291,419		316,616
Impaired Financing Receivable Related Allowance	18,482		22,086	19,417
Loans And Leases Receivable Gross Carrying Amount	3,207,981		3,290,957	3,274,340
Loans and Leases Receivable, Allowance	48,007	55,130	58,975	57,052	40,587	33,980
Residential Mortgage Loans \| PCI loans
Financing Receivable Allowance For Credit Losses [Line Items]
Loans And Leases Receivable Gross Carrying Amount	145,203		153,991	153,609
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Allowance For Loan Losses	10,954		10,873	9,863
Residential Mortgage Loans \| General Allowance [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans And Leases Receivable Gross Carrying Amount	2,653,984		2,703,532	2,694,896
Loans and Leases Receivable, Allowance	18,571		26,016	27,772
Residential Mortgage Loans \| Construction Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Impaired Financing Receivable With No Related Allowance Recorded Investment	956		0
Impaired Financing Receivable With Related Allowance Recorded Investment	809		252
Impaired Financing Receivable Related Allowance	156		55
Commercial Portfolio Segment [Member] \| Construction Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Impaired Financing Receivable With No Related Allowance Recorded Investment	0		0
Impaired Financing Receivable With Related Allowance Recorded Investment	0		35,101
Impaired Financing Receivable Related Allowance	0		560
Commercial Portfolio Segment [Member] \| Commercial And Industrial Sector [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Impaired Financing Receivable With No Related Allowance Recorded Investment	34,793		28,292
Impaired Financing Receivable With Related Allowance Recorded Investment	62,361		90,008
Impaired Financing Receivable Related Allowance	10,798		12,359	11,240
Loans And Leases Receivable Gross Carrying Amount	2,068,256		2,083,253	2,144,236
Loans and Leases Receivable, Allowance	44,166	44,000	48,871	40,379	42,082	61,953
Commercial Portfolio Segment [Member] \| Commercial And Industrial Sector [Member] \| PCI loans
Financing Receivable Allowance For Credit Losses [Line Items]
Loans And Leases Receivable Gross Carrying Amount	0		0	0
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Allowance For Loan Losses	0		0	0
Commercial Portfolio Segment [Member] \| Commercial And Industrial Sector [Member] \| General Allowance [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans And Leases Receivable Gross Carrying Amount	1,971,102		1,964,953	2,033,297
Loans and Leases Receivable, Allowance	33,368		36,512	29,139
Commercial Portfolio Segment [Member] \| Mortgage Receivable [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Impaired Financing Receivable With No Related Allowance Recorded Investment	73,433		65,100
Impaired Financing Receivable With Related Allowance Recorded Investment	169,787		87,814
Impaired Financing Receivable Related Allowance	17,044		9,783	10,456
Loans And Leases Receivable Gross Carrying Amount	1,506,502		1,614,972	1,601,638
Loans and Leases Receivable, Allowance	49,270	$ 48,718	48,493	55,943	$ 38,576	$ 57,261
Commercial Portfolio Segment [Member] \| Mortgage Receivable [Member] \| PCI loans
Financing Receivable Allowance For Credit Losses [Line Items]
Loans And Leases Receivable Gross Carrying Amount	3,919		4,183	4,185
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Allowance For Loan Losses	400		378	372
Commercial Portfolio Segment [Member] \| Mortgage Receivable [Member] \| General Allowance [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans And Leases Receivable Gross Carrying Amount	1,259,363		1,457,875	1,443,578
Loans and Leases Receivable, Allowance	31,826		38,332	$ 45,115
Finance Leases [Member] \| Consumer Loan [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Impaired Financing Receivable With No Related Allowance Recorded Investment	2,189		2,788
Impaired Financing Receivable With Related Allowance Recorded Investment	29,756		35,606
Impaired Financing Receivable Related Allowance	6,083		5,165
Loans And Leases Receivable Gross Carrying Amount	1,851,352		1,749,897
Loans and Leases Receivable, Allowance	56,041		70,982
Finance Leases [Member] \| Consumer Loan [Member] \| PCI loans
Financing Receivable Allowance For Credit Losses [Line Items]
Loans And Leases Receivable Gross Carrying Amount	0		0
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Allowance For Loan Losses	0		0
Finance Leases [Member] \| Consumer Loan [Member] \| General Allowance [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans And Leases Receivable Gross Carrying Amount	1,819,407		1,711,503
Loans and Leases Receivable, Allowance	$ 49,958		$ 65,817