Loans Receivable and Allowance for Credit Losses (Summary of Activities in Allowance for Loan Losses by Portfolio Segments and Unfunded Credit Commitments) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Allowance for loan losses by portfolio segments
Allowance, beginning of period	$ 358,287,000
Provision for (reversal of ) credit losses	73,870,000	$ 22,579,000
Gross charge-offs	0	(73,000)
Allowance, end of period	557,003,000	317,894,000
Allowance for unfunded credit commitments
Provision for (reversal of ) credit losses	73,870,000	22,579,000
Cumulative Effect, Period Of Adoption, Adjustment
Allowance for loan losses by portfolio segments
Allowance, beginning of period	125,158,000
Commercial and industrial (“C&I”)
Allowance for loan losses by portfolio segments
Gross charge-offs	(12,000,000.0)
Allowance, end of period	416,000
Allowance for Unfunded Credit Commitments
Allowance for loan losses by portfolio segments
Provision for (reversal of ) credit losses	(786,000)	1,939,000
Allowance for unfunded credit commitments
Allowance for unfunded credit commitments, beginning of period	11,158,000	12,566,000
Provision for (reversal of ) credit losses	(786,000)	1,939,000
Allowance for unfunded credit commitments, ending of period	20,829,000	$ 14,505,000
Allowance for Unfunded Credit Commitments | Cumulative Effect, Period Of Adoption, Adjustment
Allowance for unfunded credit commitments
Allowance for unfunded credit commitments, beginning of period	10,457,000
Commercial lending | Commercial and industrial (“C&I”)
Allowance for loan losses by portfolio segments
Allowance, beginning of period	238,376,000
Provision for (reversal of ) credit losses	60,618,000
Gross charge-offs	(11,977,000)
Gross recoveries	1,575,000
Total net charge-offs	(10,402,000)
Foreign currency translation adjustments	(200,000)
Allowance, end of period	362,629,000
Allowance for unfunded credit commitments
Provision for (reversal of ) credit losses	60,618,000
Commercial lending | Commercial and industrial (“C&I”) | Cumulative Effect, Period Of Adoption, Adjustment
Allowance for loan losses by portfolio segments
Allowance, beginning of period	74,237,000
Commercial lending | Commercial real estate (“CRE”)
Allowance for loan losses by portfolio segments
Allowance, beginning of period	40,509,000
Provision for (reversal of ) credit losses	11,435,000
Gross charge-offs	(954,000)
Gross recoveries	9,660,000
Total net charge-offs	8,706,000
Foreign currency translation adjustments	0
Allowance, end of period	132,819,000
Allowance for unfunded credit commitments
Provision for (reversal of ) credit losses	11,435,000
Commercial lending | Commercial real estate (“CRE”) | Cumulative Effect, Period Of Adoption, Adjustment
Allowance for loan losses by portfolio segments
Allowance, beginning of period	72,169,000
Commercial lending | Real estate loan | Multifamily residential
Allowance for loan losses by portfolio segments
Allowance, beginning of period	22,826,000
Provision for (reversal of ) credit losses	1,281,000
Gross charge-offs	0
Gross recoveries	535,000
Total net charge-offs	535,000
Foreign currency translation adjustments	0
Allowance, end of period	16,530,000
Allowance for unfunded credit commitments
Provision for (reversal of ) credit losses	1,281,000
Commercial lending | Real estate loan | Multifamily residential | Cumulative Effect, Period Of Adoption, Adjustment
Allowance for loan losses by portfolio segments
Allowance, beginning of period	(8,112,000)
Commercial lending | Construction and land
Allowance for loan losses by portfolio segments
Allowance, beginning of period	19,404,000
Provision for (reversal of ) credit losses	1,482,000
Gross charge-offs	0
Gross recoveries	21,000
Total net charge-offs	21,000
Foreign currency translation adjustments	0
Allowance, end of period	11,018,000
Allowance for unfunded credit commitments
Provision for (reversal of ) credit losses	1,482,000
Commercial lending | Construction and land | Cumulative Effect, Period Of Adoption, Adjustment
Allowance for loan losses by portfolio segments
Allowance, beginning of period	(9,889,000)
Consumer lending | Real estate loan | Single-family residential
Allowance for loan losses by portfolio segments
Allowance, beginning of period	28,527,000
Provision for (reversal of ) credit losses	1,700,000
Gross charge-offs	0
Gross recoveries	265,000
Total net charge-offs	265,000
Foreign currency translation adjustments	0
Allowance, end of period	26,822,000
Allowance for unfunded credit commitments
Provision for (reversal of ) credit losses	1,700,000
Consumer lending | Real estate loan | Single-family residential | Cumulative Effect, Period Of Adoption, Adjustment
Allowance for loan losses by portfolio segments
Allowance, beginning of period	(3,670,000)
Consumer lending | HELOCs
Allowance for loan losses by portfolio segments
Allowance, beginning of period	5,265,000
Provision for (reversal of ) credit losses	412,000
Gross charge-offs	0
Gross recoveries	2,000
Total net charge-offs	2,000
Foreign currency translation adjustments	0
Allowance, end of period	3,881,000
Allowance for unfunded credit commitments
Provision for (reversal of ) credit losses	412,000
Consumer lending | HELOCs | Cumulative Effect, Period Of Adoption, Adjustment
Allowance for loan losses by portfolio segments
Allowance, beginning of period	(1,798,000)
Consumer lending | Other consumer
Allowance for loan losses by portfolio segments
Allowance, beginning of period	3,380,000
Provision for (reversal of ) credit losses	(2,272,000)
Gross charge-offs	(26,000)
Gross recoveries	1,000
Total net charge-offs	(25,000)
Foreign currency translation adjustments	0
Allowance, end of period	3,304,000
Allowance for unfunded credit commitments
Provision for (reversal of ) credit losses	(2,272,000)
Consumer lending | Other consumer | Cumulative Effect, Period Of Adoption, Adjustment
Allowance for loan losses by portfolio segments
Allowance, beginning of period	2,221,000
Commercial and consumer lending
Allowance for loan losses by portfolio segments
Allowance, beginning of period	358,287,000
Provision for (reversal of ) credit losses	74,656,000
Gross charge-offs	(12,957,000)
Gross recoveries	12,059,000
Total net charge-offs	(898,000)
Foreign currency translation adjustments	(200,000)
Allowance, end of period	557,003,000
Allowance for unfunded credit commitments
Provision for (reversal of ) credit losses	$ 74,656,000