LOAN PORTFOLIO - Corporation's Aging of Loans Held for Investment Portfolio (Detail) - USD ($) $ in Thousands	Sep. 30, 2017		Jun. 30, 2017	Dec. 31, 2016		Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	$ 829,221			$ 881,954
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Carrying Amount	157,794		$ 160,368	165,818		$ 168,141	$ 169,690	$ 173,913
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]
Fha Va And Other Government Guaranteed Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	80,901	[1],[5],[6]		82,231	[2],[7],[8]
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Carrying Amount	0	[1],[5],[6]		0	[2],[7],[8]
Financing Receivable, Current	40,667	[1],[5],[6]		44,627	[2],[7],[8]
Loans held for investment	121,568	[1],[5],[6]		126,858	[2],[7],[8]
90 days past due and still accruing	76,601	[1],[5],[6]		77,052	[2],[7],[8]
Fha Va And Other Government Guaranteed Loans [Member] | Financing Receivables 60 To 89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	4,300	[1],[5],[6]		5,179	[2],[7],[8]
Fha Va And Other Government Guaranteed Loans [Member] | Financing Receivables 30 To 59 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	0	[1],[5],[6]		0	[2],[7],[8]
Fha Va And Other Government Guaranteed Loans [Member] | Financing Receivables Equal To Greater Than 90 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	76,601	[1],[3],[5],[6]		77,052	[2],[4],[7],[8]
Residential Mortgage [Member]
Accounts Notes And Loans Receivable [Line Items]
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Carrying Amount	153,609	[5]		162,676	[7]
Loans held for investment	3,274,340			3,296,031
Commercial And Industrial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	101,744			169,886
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Carrying Amount	0			0
Financing Receivable, Current	2,042,492			2,010,569
Loans held for investment	2,144,236			2,180,455
90 days past due and still accruing	3,653	[1]		5,368	[2]
Commercial And Industrial [Member] | Financing Receivables 60 To 89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	1,763			3,724
Commercial And Industrial [Member] | Financing Receivables 30 To 59 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	12,011			14,195
Commercial And Industrial [Member] | Financing Receivables Equal To Greater Than 90 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	87,970	[3]		151,967	[4]
Commercial Mortgage Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	159,858	[5]		186,511	[7]
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Carrying Amount	4,185	[5]		3,142	[7]
Financing Receivable, Current	1,437,595	[5]		1,379,155	[7]
Loans held for investment	1,601,638	[5]		1,568,808	[7]
90 days past due and still accruing	6,499	[1],[5]		3,281	[2],[7]
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	[5]		4,534	[7]
Commercial Mortgage Loans [Member] | Financing Receivables 30 To 59 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	0	[5]		0	[7]
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],[5]		181,977	[4],[7]
Construction Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans held for investment	129,460			124,951
Auto loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	109,316			85,011
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Carrying Amount	0			0
Financing Receivable, Current	724,896			762,947
Loans held for investment	834,212			847,958
90 days past due and still accruing	0	[1]		0	[2]
Auto loans [Member] | Financing Receivables 60 To 89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	28,638			13,523
Auto loans [Member] | Financing Receivables 30 To 59 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	64,869			57,142
Auto loans [Member] | Financing Receivables Equal To Greater Than 90 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	15,809	[3]		14,346	[4]
Finance Leases [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	17,087			10,720
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Carrying Amount	0			0
Financing Receivable, Current	228,997			222,615
Loans held for investment	246,084			233,335
90 days past due and still accruing	0	[1]		0	[2]
Finance Leases [Member] | Financing Receivables 60 To 89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	4,239			1,671
Finance Leases [Member] | Financing Receivables 30 To 59 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	10,960			7,714
Finance Leases [Member] | Financing Receivables Equal To Greater Than 90 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	1,888	[3]		1,335	[4]
Consumer Loan [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	33,778			25,257
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Carrying Amount	0			0
Financing Receivable, Current	613,466			610,078
Loans held for investment	647,244			635,335
90 days past due and still accruing	3,937	[1]		3,929	[2]
Consumer Loan [Member] | Financing Receivables 60 To 89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	5,644			5,254
Consumer Loan [Member] | Financing Receivables 30 To 59 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	15,388			7,675
Consumer Loan [Member] | Financing Receivables Equal To Greater Than 90 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	12,746	[3]		12,328	[4]
Commercial Construction [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	35,519	[5]		36,893
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Carrying Amount	0	[5]		0	[7]
Financing Receivable, Current	56,058	[5]		40,582
Loans held for investment	91,577	[5]		77,475
90 days past due and still accruing	0	[1],[5]		0	[2]
Commercial Construction [Member] | Financing Receivables 60 To 89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	0	[5]		0
Commercial Construction [Member] | Financing Receivables 30 To 59 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	0	[5]		0
Commercial Construction [Member] | Financing Receivables Equal To Greater Than 90 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	35,519	[3],[5]		36,893	[4]
Residential Construction [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	701	[5]		1,933	[7]
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Carrying Amount	0	[5]		0	[7]
Financing Receivable, Current	7,229	[5]		13,777	[7]
Loans held for investment	7,930	[5]		15,710	[7]
90 days past due and still accruing	0	[1],[5]		0	[2],[7]
Residential Construction [Member] | Financing Receivables 60 To 89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	0	[5]		0	[7]
Residential Construction [Member] | Financing Receivables 30 To 59 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	0	[5]		0	[7]
Residential Construction [Member] | Financing Receivables Equal To Greater Than 90 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	701	[3],[5]		1,933	[4],[7]
Land Construction [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	10,878	[5]		11,940	[7]
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Carrying Amount	0			0	[7]
Financing Receivable, Current	19,075	[5]		19,826	[7]
Loans held for investment	29,953	[5]		31,766	[7]
90 days past due and still accruing	215	[1],[5]		478	[2],[7]
Land Construction [Member] | Financing Receivables 60 To 89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	163	[5]		436	[7]
Land Construction [Member] | Financing Receivables 30 To 59 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	0	[5]		0	[7]
Land Construction [Member] | Financing Receivables Equal To Greater Than 90 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	10,715	[3],[5]		11,504	[4],[7]
Other Residential Mortgage Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	279,439	[5]		271,572
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Carrying Amount	153,609	[5]		162,676	[7]
Financing Receivable, Current	2,719,724	[5]		2,734,925
Loans held for investment	3,152,772	[5]		3,169,173
90 days past due and still accruing	18,646	[5]		16,701
Other Residential Mortgage Loans [Member] | Financing Receivables 60 To 89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	82,263	[5]		94,004
Other Residential Mortgage Loans [Member] | Financing Receivables 30 To 59 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	0	[5]		0
Other Residential Mortgage Loans [Member] | Financing Receivables Equal To Greater Than 90 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	$ 197,176	[3],[5]		$ 177,568

[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, 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.

[6] As of September 30, 2017, includes $45.1 million of defaulted loans collateralizing Government National Mortgage Association ("GNMA") securities for which the Corporation has an unconditional option (but not an obligation) to repurchase the defaulted loans.

[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 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.

[8] As of December 31, 2016, includes $43.7 million of defaulted loans collateralizing GNMA securities for which the Corporation has an unconditional option (but not an obligation) to repurchase the defaulted loans.