LOAN PORTFOLIO- Corporation's Aging of Purchased Credit Impaired Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2017		Dec. 31, 2016		Sep. 30, 2016
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	$ 829,221		$ 881,954
Financing Receivable, Current	7,890,199		7,839,101
Loans held for investment	8,877,214		8,886,873		$ 8,863,654
90 days past due and still accruing	109,551	[1]	106,809	[2]
Financing Receivables 60 To 89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	143,310		128,325
Financing Receivables 30 To 59 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	103,228		86,726
Financing Receivables Equal To Greater Than 90 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	582,683	[3]	666,903	[4]
Purchased Credit Impaired Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	45,886	[5]	41,246
Financing Receivable, Current	111,908	[5]	124,572
Loans held for investment	157,794	[5]	165,818
Purchased Credit Impaired Loans [Member] | Financing Receivables 60 To 89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	14,781	[5]	12,247
Purchased Credit Impaired Loans [Member] | Financing Receivables 30 To 59 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	0		0
Purchased Credit Impaired Loans [Member] | Financing Receivables Equal To Greater Than 90 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	31,105	[5]	28,999
Residential Mortgage [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans held for investment	3,274,340		3,296,031
Residential Mortgage [Member] | Purchased Credit Impaired Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	43,130	[5]	39,741	[6]
Financing Receivable, Current	110,479	[5]	122,935	[6]
Loans held for investment	153,609	[5]	162,676	[6]
30-59 Days past due Mortgages	27,500		22,300
Residential Mortgage [Member] | Purchased Credit Impaired Loans [Member] | Financing Receivables 60 To 89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	14,310	[5]	11,892	[6]
Residential Mortgage [Member] | Purchased Credit Impaired Loans [Member] | Financing Receivables 30 To 59 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	0	[5]	0	[6]
Residential Mortgage [Member] | Purchased Credit Impaired Loans [Member] | Financing Receivables Equal To Greater Than 90 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	28,820	[5]	27,849	[6]
Commercial Mortgage Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	159,858	[7]	186,511	[8]
Financing Receivable, Current	1,437,595	[7]	1,379,155	[8]
Loans held for investment	1,601,638	[7]	1,568,808	[8]
90 days past due and still accruing	6,499	[1],[7]	3,281	[2],[8]
30-59 Days past due Mortgages	33,800		4,600
Commercial Mortgage Loans [Member] | Financing Receivables 60 To 89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	16,300	[7]	4,534	[8]
Commercial Mortgage Loans [Member] | Financing Receivables 30 To 59 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	0	[7]	0	[8]
Commercial Mortgage Loans [Member] | Financing Receivables Equal To Greater Than 90 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	143,558	[3],[7]	181,977	[4],[8]
Commercial Mortgage Loans [Member] | Purchased Credit Impaired Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	2,756	[5]	1,505	[6]
Financing Receivable, Current	1,429	[5]	1,637	[6]
Loans held for investment	4,185	[5]	3,142	[6]
30-59 Days past due Mortgages	400		100
Commercial Mortgage Loans [Member] | Purchased Credit Impaired Loans [Member] | Financing Receivables 60 To 89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	471	[5]	355	[6]
Commercial Mortgage Loans [Member] | Purchased Credit Impaired Loans [Member] | Financing Receivables 30 To 59 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	0	[5]	0	[6]
Commercial Mortgage Loans [Member] | Purchased Credit Impaired Loans [Member] | Financing Receivables Equal To Greater Than 90 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	$ 2,285	[5]	$ 1,150	[6]

[1] It is the Corporation's policy to report delinquent residential mortgage loans insured by the FHA or guaranteed by the VA as past-due loans 90 days and still accruing as opposed to non-performing loans since the principal repayment is insured. These balances include $28.9 million of residential mortgage loans insured by the FHA or guaranteed by the VA that are over 15 months delinquent, and are no longer accruing interest as of September 30, 2017.

[2] It is the Corporation's policy to report delinquent residential mortgage loans insured by the FHA or guaranteed by the VA as past-due loans 90 days and still accruing as opposed to non-performing loans since the principal repayment is insured. These balances include $29.3 million of residential mortgage loans insured by the FHA or guaranteed by the VA that are over 15 months delinquent, and are no longer accruing interest as of December 31, 2016.

[3] Includes non-performing loans and accruing loans that are contractually delinquent 90 days or more (i.e., FHA/VA guaranteed loans and credit cards). Credit card loans continue to accrue finance charges and fees until charged-off at 180 days.

[4] Includes non-performing loans and accruing loans that are contractually delinquent 90 days or more (i.e. FHA/VA guaranteed loans and credit cards). Credit card loans continue to accrue finance charges and fees until charged-off at 180 days.

[5] According to the Corporation's delinquency policy and consistent with the instructions for the preparation of the Consolidated Financial Statements for Bank Holding Companies (FR Y-9C) required by the Federal Reserve Board, residential mortgage and commercial mortgage loans are considered past due when the borrower is in arrears on two or more monthly payments. PCI residential mortgage loans and commercial mortgage loans past due 30-59 days as of September 30, 2017 amounted to $27.5 million and $0.4 million, respectively.

[6] According to the Corporation's delinquency policy and consistent with the instructions for the preparation of the Consolidated Financial Statements for Bank Holding Companies (FR Y-9C) required by the Federal Reserve Board, residential mortgage and commercial mortgage loans are considered past due when the borrower is in arrears on two or more monthly payments. PCI residential mortgage loans and commercial mortgage loans past due 30-59 days as of December 31, 2016 amounted to $22.3 million and $0.1 million, respectively.

[7] According to the Corporation's delinquency policy and consistent with the instructions for the preparation of the Consolidated Financial Statements for Bank Holding Companies (FR Y-9C) required by the Federal Reserve Board, residential mortgage, commercial mortgage, and construction loans are considered past due when the borrower is in arrears on two or more monthly payments. FHA/VA government-guaranteed loans, other residential mortgage loans, commercial mortgage loans, land loans, construction-residential loans and construction-commercial loans past due 30-59 days as of September 30, 2017 amounted to $9.4 million, $216.1 million, $33.8 million, $0.9 million, $6.4 million and $0.1 million, respectively.

[8] According to the Corporation's delinquency policy and consistent with the instructions for the preparation of the Consolidated Financial Statements for Bank Holding Companies (FR Y-9C) required by the Federal Reserve Board, residential mortgage, commercial mortgage, and construction loans are considered past due when the borrower is in arrears on two or more monthly payments. FHA/VA government-guaranteed loans, other residential mortgage loans, commercial mortgage loans, land loans and construction-residential loans past due 30-59 days as of December 31, 2016 amounted to $9.9 million, $142.8 million, $4.6 million, $0.7 million and $0.4 million, respectively.