Loans - Additional Information (Detail) (USD $)	3 Months Ended		12 Months Ended					12 Months Ended						3 Months Ended				12 Months Ended	9 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Non-officer directors	Dec. 31, 2012 Non-officer directors	Dec. 31, 2013 Covered Loans	Dec. 31, 2012 Covered Loans	Dec. 31, 2011 Covered Loans	Dec. 31, 2013 Financing Receivable Troubled Debt Restructurings Rate Reductions	Dec. 31, 2013 Financing Receivable Troubled Debt Restructurings Forbearance Of Arrears	Dec. 31, 2013 Commercial Real Estate Loan	Jun. 30, 2013 Commercial Real Estate Impaired Loans	Mar. 31, 2013 Commercial Real Estate Impaired Loans	Dec. 31, 2013 Total non-accrual mortgage loans	Dec. 31, 2012 Total non-accrual mortgage loans	Dec. 31, 2013 Multi-Family Loan	Sep. 30, 2013 Multi-Family Impaired Loans	Dec. 31, 2013 Multi-Family Impaired Loans	Jun. 30, 2013 Multi-Family Non-Accrual	Dec. 31, 2013 Commercial and Industrial Loan	Dec. 31, 2013 Am Trust Bank and Desert Hills Bank	Dec. 31, 2012 Am Trust Bank and Desert Hills Bank
Financing Receivable, Recorded Investment [Line Items]
Outstanding loans to non-officer directors						$ 149,400,000	$ 128,000,000
Unpaid principal balance of serviced loans																21,500,000,000	17,600,000,000
Delinquent loans selectively extended to certain borrowers, rate reductions, forbearance of arrears, and extension of maturity dates											72,900,000	7,400,000
Decline in loans														23,500,000	35,300,000				56,000,000	64,000,000
Transfer of loan																					49,600,000
Transfer of loan to other real estate owned		41,600,000
Satisfaction of loan relationship	22,000,000		50,600,000
Number of loans classified as a non-accrual TDRs													1					1				2
Loan classified as non accrual TDRs													1,100,000					3,900,000				758,000
Total loans, net			32,727,507,000	31,580,636,000																			3,300,000,000	3,900,000,000
Covered loans			2,788,618,000	3,284,061,000
Total loans 30-89 days past due								57,929,000	81,186,000
Total covered loans 90 days or more past due								211,485,000	312,573,000
Covered loan portfolio, current								2,500,000,000
Provision for losses on loans			30,758,000	62,988,000	100,420,000			12,758,000	17,988,000	21,420,000
FDIC indemnification income			$ 10,200,000	$ 14,400,000