Loans - Additional Information (Detail) (USD $)	3 Months Ended			6 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Total loans, net	$ 31,638,995,000			$ 31,638,995,000		$ 31,580,636,000
Covered loans	3,032,172,000			3,032,172,000		3,284,061,000
Provision for losses on loans	9,618,000		33,448,000	19,120,000	48,448,000
FDIC indemnification income	3,700,000	3,600,000		7,300,000
Covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans 30-89 days past due	65,391,000			65,391,000		81,186,000
Total covered loans 90 days or more past due	267,821,000			267,821,000		312,573,000
Covered loan portfolio, current	2,700,000,000			2,700,000,000
Provision for losses on loans	4,618,000		18,448,000	9,120,000	18,448,000
Financing Receivable Troubled Debt Restructurings Rate Reductions
Financing Receivable, Recorded Investment [Line Items]
Delinquent loans selectively extended to certain borrowers, rate reductions, forbearance of arrears, and extension of maturity dates				114,200,000
Financing Receivable Troubled Debt Restructurings Forbearance Of Arrears
Financing Receivable, Recorded Investment [Line Items]
Delinquent loans selectively extended to certain borrowers, rate reductions, forbearance of arrears, and extension of maturity dates				10,200,000
Total non-accrual mortgage loans
Financing Receivable, Recorded Investment [Line Items]
Unpaid principal balance of serviced loans	20,500,000,000			20,500,000,000		17,600,000,000
Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Satisfaction of loan relationship				22,000,000
Number of loans classified as a non-accrual TDRs				2
Loan classified as non accrual TDRs	1,700,000			1,700,000
Commercial Real Estate | Accruing
Financing Receivable, Recorded Investment [Line Items]
Decline in loans		35,200,000
Commercial Real Estate | Non-Accrual
Financing Receivable, Recorded Investment [Line Items]
Decline in loans				22,500,000
Am Trust Bank and Desert Hills Bank
Financing Receivable, Recorded Investment [Line Items]
Total loans, net	$ 3,600,000,000			$ 3,600,000,000		$ 3,900,000,000