COVERED ASSETS AND FDIC INDEMNIFICATION ASSET, Covered Assets and Credit Quality Indicators (Details) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010	Sep. 30, 2011		Sep. 30, 2010	Dec. 31, 2010
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	$ 5,018,267,000			$ 5,018,267,000			$ 5,955,773,000
Covered discount	(871,931,000)			(871,931,000)			(1,150,672,000)
Net valuation of loans	4,146,336,000			4,146,336,000			4,805,101,000
Allowance on covered loans	(6,434,000)			(6,434,000)			(4,225,000)
Total covered loans, net	4,139,902,000			4,139,902,000			4,800,876,000
Covered Nonperforming Assets [Abstract]
Covered nonaccrual loans	245,986,000	[1]		245,986,000	[1]		379,797,000	[1]
Number of covered OREO properties	92			92			114
Covered loans past due 90 days or more but not on nonaccrual	0			0			0
Total nonperforming loans	245,986,000			245,986,000			379,797,000
Other real estate owned covered, net	87,298,000			87,298,000			123,902,000
Percentage of covered OREO properties located in California (in hundredths)	67.00%			67.00%
Percentage of covered OREO properties located in Washington (in hundredths)	26.00%			26.00%
Number of covered OREO properties added during the period				103
Aggregate carrying value of covered OREO properties sold during the period				79,900,000
Amount of net writedowns included in aggregate carrying value on covered OREO properties				18,100,000
Number of covered OREO properties sold during the period				125
Total carrying value of covered OREO properties sold during the period				63,200,000
Combined net gains (losses) on covered OREO properties sold during the period				633,000
Total covered nonperforming assets	333,284,000			333,284,000			503,699,000
Balance at beginning of period	980,932,000		986,389,000	1,153,272,000		983,107,000
Additions	0		0	0		84,556,000
Accretion	(51,307,000)		(3,601,000)	(162,746,000)		(11,118,000)
Changes in expected cash flows	(49,581,000)		(24,314,000)	(110,481,000)		(98,071,000)
Balance at end of period	880,045,000		958,474,000	880,045,000		958,474,000
Business Acquisition [Line Items]
Number of days following the 10th anniversary of the acquisition date upon which the Company will be required to pay a calculated amount to the FDIC (in days)	45D			45D
Term of commercial loan shared-loss agreement (in years)	5Y			5Y
Term of single-family residential mortgage loan shared-loss agreement (in years)	10Y			10Y
Term of loss recovery provisions for commercial loans (in years)	8Y			8Y
Term of loss recovery provisions for single-family residential mortgage loans (in years)	10Y			10Y
Percentage of excess resulting from the calculation of liability to the FDIC (in hundredths)	50.00%			50.00%
Percentage of the Intrinsic Loss Estimate used in the calculation of the liability to the FDIC (in hundredths)	20.00%			20.00%
Percentage of the asset discount used in the calculation of the liability to the FDIC (in hundredths)	25.00%			25.00%
Percentage of the Cumulative Shared-Loss Payments used in the calculation of the liability to the FDIC (in hundredths)	25.00%			25.00%
Covered Loans Not Accounted For Under ASC 310-30 [Line Items]
Estimated liability for WFIB and UCB that will be due to the FDIC based on specific thresholds of losses not being reached	10,700,000			10,700,000			7,100,000
Credit Quality Indicators [Abstract]
Additional advances under shared-loss agreements	586,600,000			586,600,000
Total allowance allocated to additional advances	6,400,000			6,400,000
Percentage of allowance allocated to additional advances	2.90%			2.90%
Real Estate Loans [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	4,032,337,000			4,032,337,000			4,776,263,000
Real Estate Loans [Member] | Residential Single-family [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	470,368,000			470,368,000			553,541,000
Real Estate Loans [Member] | Residential Single-family [Member] | Pass/Watch [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	445,223,000			445,223,000			525,979,000
Real Estate Loans [Member] | Residential Single-family [Member] | Special Mention [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	2,586,000			2,586,000			2,153,000
Real Estate Loans [Member] | Residential Single-family [Member] | Substandard [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	22,559,000			22,559,000			25,157,000
Real Estate Loans [Member] | Residential Single-family [Member] | Doubtful [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	0			0			252,000
Real Estate Loans [Member] | Residential Multifamily [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	959,188,000			959,188,000			1,093,331,000
Real Estate Loans [Member] | Residential Multifamily [Member] | Pass/Watch [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	785,022,000			785,022,000			1,008,274,000
Real Estate Loans [Member] | Residential Multifamily [Member] | Special Mention [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	31,755,000			31,755,000			15,114,000
Real Estate Loans [Member] | Residential Multifamily [Member] | Substandard [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	142,411,000			142,411,000			67,366,000
Real Estate Loans [Member] | Residential Multifamily [Member] | Doubtful [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	0			0			2,577,000
Real Estate Loans [Member] | Commercial and Industrial Real Estate [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	1,883,843,000			1,883,843,000			2,085,674,000
Real Estate Loans [Member] | Commercial and Industrial Real Estate [Member] | Pass/Watch [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	1,304,704,000			1,304,704,000			1,520,135,000
Real Estate Loans [Member] | Commercial and Industrial Real Estate [Member] | Special Mention [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	47,389,000			47,389,000			89,870,000
Real Estate Loans [Member] | Commercial and Industrial Real Estate [Member] | Substandard [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	523,480,000			523,480,000			466,588,000
Real Estate Loans [Member] | Commercial and Industrial Real Estate [Member] | Doubtful [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	8,270,000			8,270,000			9,081,000
Real Estate Loans [Member] | Construction and Land [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	718,938,000			718,938,000			1,043,717,000
Real Estate Loans [Member] | Construction and Land [Member] | Pass/Watch [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	251,416,000			251,416,000			328,214,000
Real Estate Loans [Member] | Construction and Land [Member] | Special Mention [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	42,955,000			42,955,000			125,688,000
Real Estate Loans [Member] | Construction and Land [Member] | Substandard [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	418,318,000			418,318,000			556,070,000
Real Estate Loans [Member] | Construction and Land [Member] | Doubtful [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	6,249,000			6,249,000			33,745,000
Real Estate Loans [Member] | Pass/Watch [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	2,786,365,000			2,786,365,000			3,382,602,000
Real Estate Loans [Member] | Special Mention [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	124,685,000			124,685,000			232,825,000
Real Estate Loans [Member] | Substandard [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	1,106,768,000			1,106,768,000			1,115,181,000
Real Estate Loans [Member] | Doubtful [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	14,519,000			14,519,000			45,655,000
Other Loans [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	985,930,000			985,930,000			1,179,510,000
Other Loans [Member] | Commercial Business [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	884,772,000			884,772,000			1,072,020,000
Other Loans [Member] | Commercial Business [Member] | Pass/Watch [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	665,944,000			665,944,000			834,252,000
Other Loans [Member] | Commercial Business [Member] | Special Mention [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	41,116,000			41,116,000			64,702,000
Other Loans [Member] | Commercial Business [Member] | Substandard [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	169,913,000			169,913,000			161,401,000
Other Loans [Member] | Commercial Business [Member] | Doubtful [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	7,799,000			7,799,000			11,665,000
Other Loans [Member] | Other Consumer [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	101,158,000			101,158,000			107,490,000
Other Loans [Member] | Other Consumer [Member] | Pass/Watch [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	99,350,000			99,350,000			106,232,000
Other Loans [Member] | Other Consumer [Member] | Special Mention [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	176,000			176,000			336,000
Other Loans [Member] | Other Consumer [Member] | Substandard [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	1,632,000			1,632,000			922,000
Other Loans [Member] | Other Consumer [Member] | Doubtful [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	0			0			0
Other Loans [Member] | Pass/Watch [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	765,294,000			765,294,000			940,484,000
Other Loans [Member] | Special Mention [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	41,292,000			41,292,000			65,038,000
Other Loans [Member] | Substandard [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	171,545,000			171,545,000			162,323,000
Other Loans [Member] | Doubtful [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	7,799,000			7,799,000			11,665,000
Pass/Watch [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	3,551,659,000			3,551,659,000			4,323,086,000
Special Mention [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	165,977,000			165,977,000			297,863,000
Substandard [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	1,278,313,000			1,278,313,000			1,277,504,000
Doubtful [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	22,318,000			22,318,000			57,320,000
Washington First International Bank [Member]
Business Acquisition [Line Items]
Percentage of loans receivable acquired covered by shared-loss agreements (in hundredths)	99.00%			99.00%
Percentage of eligible losses for which the FDIC is obligated to reimburse the Company (in hundredths)	80.00%			80.00%
Minimum percentage obligation to reimburse the FDIC for eligible recoveries related to covered assets (in hundredths)	80.00%			80.00%
United Commercial Bank [Member]
Business Acquisition [Line Items]
Percentage of loans receivable acquired covered by shared-loss agreements (in hundredths)	100.00%			100.00%
Percentage of eligible losses for which the FDIC is obligated to reimburse the Company (in hundredths)	80.00%			80.00%
Minimum percentage obligation to reimburse the FDIC for eligible recoveries related to covered assets (in hundredths)	80.00%			80.00%
Percentage of eligible losses in excess of a specified amount for which the FDIC is obligated to reimburse the Company (in hundredths)	95.00%			95.00%
Amount of eligible losses over which the FDIC is obligated to reimburse a higher percentage	2,050,000,000			2,050,000,000
Maximum percentage obligation to reimburse the FDIC for eligible recoveries related to covered assets (in hundredths)	95.00%			95.00%
Commercial and Industrial [Member]
Credit Quality Indicators [Abstract]
Additional advances under shared-loss agreements	383,100,000			383,100,000
Total allowance allocated to additional advances	2,400,000			2,400,000
Commercial Real Estate [Member]
Credit Quality Indicators [Abstract]
Additional advances under shared-loss agreements	164,500,000			164,500,000
Total allowance allocated to additional advances	3,800,000			3,800,000
Consumer [Member]
Credit Quality Indicators [Abstract]
Additional advances under shared-loss agreements	29,200,000			29,200,000
Total allowance allocated to additional advances	167,000			167,000
Residential [Member]
Credit Quality Indicators [Abstract]
Additional advances under shared-loss agreements	9,800,000			9,800,000
Total allowance allocated to additional advances	$ 74,000			$ 74,000

[1] Covered nonaccrual loans meet the criteria for nonaccrual but have a yield accreted through interest income under ASC 310-30.