Note Loans - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Assets Obtained As Proceeds	$ 119,962	$ 176,092	$ 260,619	$ 353,182
Loans and Leases Receivable, Gross, Carrying Amount, Covered	0		0			$ 517,274
Loans transfer to non-covered status					$ 514,600
Mortgage loans related to buy-back option program	24,752,700		24,752,700			24,423,427
Non-covered Loans held-in-portfolio	24,608,516		24,608,516			24,292,794
Buy back option program
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing loans past-due 90 days or more	298,000		298,000			840,000
Mortgage loans related to buy-back option program	298,000		298,000			840,000
GNMA
Accounts, Notes, Loans and Financing Receivable [Line Items]
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Assets Obtained As Proceeds	97,000	136,000	210,000	283,000
FNMA
Accounts, Notes, Loans and Financing Receivable [Line Items]
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Assets Obtained As Proceeds	20,000	37,000	46,000	65,000
Residential Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Residential Mortgage Loans Sold	16,000	26,000	26,000	54,000
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchase of Loans	53,000	108,000	105,000	150,000
Non-covered Loans held-in-portfolio	3,841,141		3,841,141			3,810,527
Credit cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered Loans held-in-portfolio	1,079,603		1,079,603			1,093,321
Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchase of Loans	177,000	$ 124,000	333,000	260,000
Non-covered Loans held-in-portfolio	7,376,711		7,376,711			7,270,407
Mortgages | US Government Agency Insured Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered Loans held-in-portfolio	1,500,000		1,500,000			1,800,000
Mortgages | US Government Agency Insured Loans | Past Due 90 Days or More
Accounts, Notes, Loans and Financing Receivable [Line Items]
Past Due	877,000		877,000			1,200,000
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered Loans held-in-portfolio	899,323		899,323			880,029
Leasing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchase of Loans				$ 2,000
Non-covered Loans held-in-portfolio	872,098		872,098			809,990
Reverse Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	66,000		66,000			58,000
Residential mortgage loans insured By FHA
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing loans past-due 90 days or more	216,000		216,000			178,000
ASC Subtopic 310-30
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding principal balance of SOP loans	$ 2,300,000		$ 2,300,000			$ 2,500,000