COVERED ASSETS AND FDIC INDEMNIFICATION ASSET, Covered Assets and Credit Quality Indicators (Details) (USD $)	3 Months Ended			6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010	Jun. 30, 2011		Jun. 30, 2010	Dec. 31, 2010
Business Acquisition [Line Items]
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
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
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%
Estimated liability for WFIB and UCB that will be due to the FDIC based on specific thresholds of losses not being reached	$ 7,000,000			$ 7,000,000
Credit Quality Indicators [Abstract]
Additional advances under shared-loss agreements	607,500,000			607,500,000
Total allowance allocated to additional advances	6,700,000			6,700,000
Percentage of allowance allocated to additional advances	3.10%			3.10%
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	5,309,627,000			5,309,627,000			5,955,773,000
Covered discount	(946,301,000)			(946,301,000)			(1,150,672,000)
Net valuation of loans	4,363,301,000			4,363,301,000			4,805,101,000
Allowance on covered loans	(6,731,000)			(6,731,000)			(4,225,000)
Total covered loans, net	4,356,595,000			4,356,595,000			4,880,876,000
Covered Nonperforming Assets [Abstract]
Covered nonaccrual loans	242,106,000	[1]		242,106,000	[1]		379,797,000	[1]
Covered loans past due 90 days or more but not on nonaccrual	0			0			0
Total nonperforming loans	242,106,000			242,106,000			379,797,000
Other real estate owned covered, net	123,050,000			123,050,000			123,902,000
Total covered nonperforming assets	365,156,000			365,156,000			503,699,000
Number of covered OREO properties	98			98			114
Percentage of covered OREO properties located in California (in hundredths)	61.00%			61.00%
Percentage of covered OREO properties located in Washington (in hundredths)	32.00%			32.00%
Number of covered OREO properties added during the period				70
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				86
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
Changes in the accretable yield for the covered loans [Rollforward]
Balance at beginning of period	1,068,116,000		771,549,000	1,153,272,000		983,107,000
Additions	0		84,556,000	0		84,556,000
Accretion	(52,760,000)		(3,664,000)	(111,440,000)		(7,517,000)
Cash receipts, disposals and changes in expected cash flows	(34,424,000)		133,948,000	(60,900,000)		(73,757,000)
Balance at end of period	980,932,000		986,389,000	980,932,000		986,389,000
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%
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
Minimum percentage obligation to reimburse the FDIC for eligible recoveries related to covered assets (in hundredths)	80.00%			80.00%
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	400,100,000			400,100,000
Total allowance allocated to additional advances	2,700,000			2,700,000
Commercial Real Estate [Member]
Credit Quality Indicators [Abstract]
Additional advances under shared-loss agreements	167,200,000			167,200,000
Total allowance allocated to additional advances	3,800,000			3,800,000
Consumer [Member]
Credit Quality Indicators [Abstract]
Additional advances under shared-loss agreements	28,700,000			28,700,000
Total allowance allocated to additional advances	168,000			168,000
Residential [Member]
Credit Quality Indicators [Abstract]
Additional advances under shared-loss agreements	11,500,000			11,500,000
Total allowance allocated to additional advances	77,000			77,000
Real Estate Loans [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	4,256,098,000			4,256,098,000			4,776,263,000
Real Estate Loans [Member] | Residential Single-family [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	497,846,000			497,846,000			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	469,239,000			469,239,000			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	1,387,000			1,387,000			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	27,220,000			27,220,000			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	1,008,114,000			1,008,114,000			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	837,517,000			837,517,000			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	29,981,000			29,981,000			15,114,000
Real Estate Loans [Member] | Residential Multifamily [Member] | Substandard [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	140,616,000			140,616,000			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	1,958,440,000			1,958,440,000			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	1,376,656,000			1,376,656,000			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	54,765,000			54,765,000			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	518,267,000			518,267,000			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	8,752,000			8,752,000			9,081,000
Real Estate Loans [Member] | Construction and Land [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	791,698,000			791,698,000			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	252,088,000			252,088,000			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	67,798,000			67,798,000			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	462,774,000			462,774,000			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	9,038,000			9,038,000			33,745,000
Real Estate Loans [Member] | Pass/Watch [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	2,935,500,000			2,935,500,000			3,382,602,000
Real Estate Loans [Member] | Special Mention [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	153,931,000			153,931,000			232,825,000
Real Estate Loans [Member] | Substandard [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	1,148,877,000			1,148,877,000			1,115,181,000
Real Estate Loans [Member] | Doubtful [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	17,790,000			17,790,000			45,655,000
Other Loans [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	1,053,529,000			1,053,529,000			1,179,510,000
Other Loans [Member] | Commercial Business [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	949,368,000			949,368,000			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	727,980,000			727,980,000			834,252,000
Other Loans [Member] | Commercial Business [Member] | Special Mention [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	65,216,000			65,216,000			64,702,000
Other Loans [Member] | Commercial Business [Member] | Substandard [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	147,463,000			147,463,000			161,401,000
Other Loans [Member] | Commercial Business [Member] | Doubtful [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	8,709,000			8,709,000			11,665,000
Other Loans [Member] | Other Consumer [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	104,161,000			104,161,000			107,490,000
Other Loans [Member] | Other Consumer [Member] | Pass/Watch [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	102,713,000			102,713,000			106,232,000
Other Loans [Member] | Other Consumer [Member] | Special Mention [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	218,000			218,000			336,000
Other Loans [Member] | Other Consumer [Member] | Substandard [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	1,230,000			1,230,000			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	830,693,000			830,693,000			940,484,000
Other Loans [Member] | Special Mention [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	65,434,000			65,434,000			65,038,000
Other Loans [Member] | Substandard [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	148,693,000			148,693,000			162,323,000
Other Loans [Member] | Doubtful [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	8,709,000			8,709,000			11,665,000
Pass/Watch [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	3,766,193,000			3,766,193,000			4,323,086,000
Special Mention [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	219,365,000			219,365,000			297,863,000
Substandard [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	1,297,570,000			1,297,570,000			1,277,504,000
Doubtful [Member]
Carrying Amounts And Composition Of Covered Loans [Line Items]
Total principal balance	$ 26,499,000			$ 26,499,000			$ 57,320,000

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