Loans Held for Investment, net - Additional Information (Detail)	9 Months Ended	12 Months Ended
	Dec. 31, 2013 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($) Dwellings
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest rate of loans, minimum		2.00%
Interest rate of loans, maximum		6.00%
Percentage of portion of loans collateralized by real estate		99.00%
Non-accrual loans	$ 1,621,554,000	$ 1,640,853,000	$ 1,573,020,000
Transfer of loans to OREO	19,352,000	$ 3,256,000	10,381,000
Guarantee provided by government agencies against outstanding balances of education loans		97.00%
Loans modified in TDR		$ 0	0
Unpaid principal of various loans receivable		661,800,000	726,600,000
Loans granted to officers, directors and affiliates		16,000	$ 49,000
Principal additions to granted loan		0
Principal loan amount, net		$ 33,000
Period for loans deemed as non-accrual to return to accrual status		90 days	90 days
Non-accrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans		$ 15,309,000	$ 35,115,000
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans , amount		$ 319,000,000
Gross loans, percentage		19.50%
Corporation's share of interest income		11.00%
Corporation's share of interchanging income		25.00%
Outstanding credit card balances		$ 6,600,000
Gains (loss) on sales of credit card		0
Non-accrual loans	367,831,000	318,954,000	341,866,000
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans , amount		$ 25,200,000
Gross loans, percentage		1.50%
Non-accrual loans	$ 21,591,000	$ 25,199,000	16,514,000
Education
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due ninety days or more and still accruing		6,200,000
Education | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans		91,671,000	$ 108,384,000
Residential Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans , amount		$ 529,800,000
Gross loans, percentage		32.30%
Residential Loans | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of dwellings | Dwellings			1
Residential Loans | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of dwellings | Dwellings			4
Adjustable Rate Residential Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans , amount		$ 305,700,000
Gross loans, percentage		57.70%
Term of loans		30 years
Fixed-rate residential loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans , amount		$ 224,100,000
Gross loans, percentage		42.30%
Fixed-rate residential loans | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term of loans		10 years
Fixed-rate residential loans | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term of loans		30 years
Education Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans , amount		$ 91,700,000
Gross loans, percentage		5.60%
Sale of loans		$ 0	$ 0
Education Loans | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Guarantee given for principal amount and interest rate of loans, percentage		97.00%
Real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans , amount		$ 766,900,000
Gross loans, percentage		46.70%