Loans Receivable and Allowance for Credit Losses (Summary of Activities in Allowance for Loan Losses) (Details) - USD ($) $ in Thousands		12 Months Ended
	Jan. 01, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for loan losses
Allowance for loan losses, beginning of period	$ 311,322	$ 358,287	$ 311,322	$ 287,128
Provision for credit losses		210,653	98,685	64,255
Gross charge-offs		(81,837)	(75,067)	(59,433)
Gross recoveries		18,672	22,264	19,363
Total net (charge-offs) recoveries		(63,165)	(52,803)	(40,070)
Foreign currency translation adjustment		1,012	(325)	(743)
Allowance for loan losses, end of period		$ 619,983	358,287	311,322
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201602Member	us-gaap:AccountingStandardsUpdate201613Member
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13
Allowance for loan losses
Allowance for loan losses, beginning of period		$ 125,158
Allowance for loan losses, end of period			125,158
Commercial Lending | C&I
Allowance for loan losses
Allowance for loan losses, beginning of period	$ 189,117	238,376	189,117	163,058
Provision for credit losses		145,212	109,068	75,629
Gross charge-offs		(66,225)	(73,985)	(59,244)
Gross recoveries		5,428	14,501	10,417
Total net (charge-offs) recoveries		(60,797)	(59,484)	(48,827)
Foreign currency translation adjustment		1,012	(325)	(743)
Allowance for loan losses, end of period		398,040	238,376	189,117
Commercial Lending | C&I | Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13
Allowance for loan losses
Allowance for loan losses, beginning of period		74,237
Allowance for loan losses, end of period			74,237
Commercial Lending | CRE
Allowance for loan losses
Allowance for loan losses, beginning of period	40,666	40,509	40,666	40,809
Provision for credit losses		55,864	(4,345)	(5,337)
Gross charge-offs		(15,206)	(1,021)	0
Gross recoveries		10,455	5,209	5,194
Total net (charge-offs) recoveries		(4,751)	4,188	5,194
Foreign currency translation adjustment		0	0	0
Allowance for loan losses, end of period		163,791	40,509	40,666
Commercial Lending | CRE | Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13
Allowance for loan losses
Allowance for loan losses, beginning of period		72,169
Allowance for loan losses, end of period			72,169
Commercial Lending | Residential loan | Multifamily
Allowance for loan losses
Allowance for loan losses, beginning of period	19,885	22,826	19,885	19,537
Provision for credit losses		10,879	1,085	(1,409)
Gross charge-offs		0	0	0
Gross recoveries		1,980	1,856	1,757
Total net (charge-offs) recoveries		1,980	1,856	1,757
Foreign currency translation adjustment		0	0	0
Allowance for loan losses, end of period		27,573	22,826	19,885
Commercial Lending | Residential loan | Multifamily | Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13
Allowance for loan losses
Allowance for loan losses, beginning of period		(8,112)
Allowance for loan losses, end of period			(8,112)
Commercial Lending | Construction and land
Allowance for loan losses
Allowance for loan losses, beginning of period	20,290	19,404	20,290	26,881
Provision for credit losses		644	(1,422)	(7,331)
Gross charge-offs		0	0	0
Gross recoveries		80	536	740
Total net (charge-offs) recoveries		80	536	740
Foreign currency translation adjustment		0	0	0
Allowance for loan losses, end of period		10,239	19,404	20,290
Commercial Lending | Construction and land | Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13
Allowance for loan losses
Allowance for loan losses, beginning of period		(9,889)
Allowance for loan losses, end of period			(9,889)
Consumer Lending | Residential loan | Single-family
Allowance for loan losses
Allowance for loan losses, beginning of period	31,340	28,527	31,340	26,362
Provision for credit losses		(9,922)	(2,938)	3,765
Gross charge-offs		0	(11)	(1)
Gross recoveries		585	136	1,214
Total net (charge-offs) recoveries		585	125	1,213
Foreign currency translation adjustment		0	0	0
Allowance for loan losses, end of period		15,520	28,527	31,340
Consumer Lending | Residential loan | Single-family | Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13
Allowance for loan losses
Allowance for loan losses, beginning of period		(3,670)
Allowance for loan losses, end of period			(3,670)
Consumer Lending | HELOCs
Allowance for loan losses
Allowance for loan losses, beginning of period	5,774	5,265	5,774	7,354
Provision for credit losses		(605)	(516)	(1,618)
Gross charge-offs		(221)	0	0
Gross recoveries		49	7	38
Total net (charge-offs) recoveries		(172)	7	38
Foreign currency translation adjustment		0	0	0
Allowance for loan losses, end of period		2,690	5,265	5,774
Consumer Lending | HELOCs | Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13
Allowance for loan losses
Allowance for loan losses, beginning of period		(1,798)
Allowance for loan losses, end of period			(1,798)
Consumer Lending | Other consumer
Allowance for loan losses
Allowance for loan losses, beginning of period	$ 4,250	3,380	4,250	3,127
Provision for credit losses		(3,381)	(839)	1,308
Gross charge-offs		(185)	(50)	(188)
Gross recoveries		95	19	3
Total net (charge-offs) recoveries		(90)	(31)	(185)
Foreign currency translation adjustment		0	0	0
Allowance for loan losses, end of period		2,130	3,380	4,250
Consumer Lending | Other consumer | Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13
Allowance for loan losses
Allowance for loan losses, beginning of period		2,221
Allowance for loan losses, end of period			2,221
Commercial and Consumer Portfolio Segment
Allowance for loan losses
Provision for credit losses		198,691	100,093	$ 65,007
Non-PCI loans
Allowance for loan losses
Allowance for loan losses, beginning of period		358,287
Allowance for loan losses, end of period			358,287
PCI Loans
Allowance for loan losses
Allowance for loan losses, beginning of period		$ 0
Allowance for loan losses, end of period			$ 0