Loans Receivable and Allowance for Credit Losses (Summary of Activities in Allowance for Credit Losses) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Allowance for loan losses
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
Commercial and industrial (“C&I”)
Allowance for loan losses
Gross Charge-offs	(12,000,000.0)
Allowance, end of period	416,000
Unfunded Credit Commitments
Allowance for loan losses
Provision for (reversal of ) credit losses	(786,000)	1,939,000
Allowance for unfunded credit commitments, beginning of period	11,158,000	12,566,000
Allowance for unfunded credit commitments, ending of period	20,829,000	14,505,000
Commercial lending | Commercial and industrial (“C&I”)
Allowance for loan losses
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
Commercial lending | Commercial real estate (“CRE”)
Allowance for loan losses
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
Commercial lending | Real estate loan | Multifamily residential
Allowance for loan losses
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
Commercial lending | Construction and land
Allowance for loan losses
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
Consumer lending | Other consumer
Allowance for loan losses
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
Consumer lending | Real estate loan | Single-family residential
Allowance for loan losses
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
Consumer lending | HELOCs
Allowance for loan losses
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
Non-PCI Loans
Allowance for loan losses
Allowance, beginning of period	358,287,000	311,300,000
Provision for (reversal of ) credit losses		20,648,000
Gross Charge-offs		(17,258,000)
Gross recoveries		2,821,000
Total net charge-offs		(14,437,000)
Foreign currency translation adjustments		369,000
Allowance, end of period		317,880,000
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”)
Allowance for loan losses
Gross Charge-offs		(17,244,000)
Gross recoveries		2,251,000
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”)
Allowance for loan losses
Gross recoveries		222,000
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily residential
Allowance for loan losses
Gross recoveries		281,000
Non-PCI Loans | Commercial lending | Construction and land
Allowance for loan losses
Gross recoveries		63,000
Non-PCI Loans | Commercial lending | Total CRE
Allowance for loan losses
Gross recoveries		566,000
Non-PCI Loans | Consumer lending | Other consumer
Allowance for loan losses
Gross Charge-offs		(14,000)
Non-PCI Loans | Consumer lending | Real estate loan | Single-family residential
Allowance for loan losses
Gross recoveries		2,000
Non-PCI Loans | Consumer lending | HELOCs
Allowance for loan losses
Gross recoveries		2,000
Non-PCI Loans | Consumer lending | Total residential mortgage
Allowance for loan losses
Gross recoveries		4,000
PCI Loans
Allowance for loan losses
Allowance, beginning of period	0	22,000
Provision for (reversal of ) credit losses		(8,000)
Allowance, end of period		$ 14,000
PCI Loans | Commercial lending | Commercial and industrial (“C&I”)
Allowance for loan losses
Allowance, beginning of period	0
PCI Loans | Commercial lending | Commercial real estate (“CRE”)
Allowance for loan losses
Allowance, beginning of period	0
PCI Loans | Commercial lending | Real estate loan | Multifamily residential
Allowance for loan losses
Allowance, beginning of period	0
PCI Loans | Commercial lending | Construction and land
Allowance for loan losses
Allowance, beginning of period	0
PCI Loans | Consumer lending | Other consumer
Allowance for loan losses
Allowance, beginning of period	0
PCI Loans | Consumer lending | Real estate loan | Single-family residential
Allowance for loan losses
Allowance, beginning of period	0
PCI Loans | Consumer lending | HELOCs
Allowance for loan losses
Allowance, beginning of period	$ 0