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		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019		Dec. 31, 2018
Financing Receivable Allowance for Credit Losses
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate201613Member		us-gaap:AccountingStandardsUpdate201613Member	[1]	us-gaap:AccountingStandardsUpdate201602Member	[2]
Allowance for loan losses by portfolio segments
Allowance, beginning of period			$ 358,287,000
Provision for credit losses	$ 102,443,000	$ 19,245,000	176,313,000	$ 41,824,000
Gross charge-offs	0	(317,000)	0	(390,000)
Allowance, end of period	632,071,000		632,071,000		$ 358,287,000
Allowance for unfunded credit commitments
Provision for (reversal of) credit losses on unfunded credit commitments	102,443,000	19,245,000	176,313,000	41,824,000
PCD or PCI loans
Allowance for loan losses by portfolio segments
Allowance, beginning of period			0
Allowance, end of period					0
Commercial and industrial (“C&I”)
Allowance for loan losses by portfolio segments
Allowance, end of period	756,000		756,000
HELOCs
Allowance for loan losses by portfolio segments
Allowance, end of period	76,000		76,000
Unfunded Credit Commitments
Allowance for loan losses by portfolio segments
Provision for credit losses	8,143,000	(1,486,000)	7,357,000	453,000
Allowance for unfunded credit commitments
Allowance for Unfunded Credit Commitments	20,829,000	14,505,000	11,158,000	12,566,000	12,566,000
Provision for (reversal of) credit losses on unfunded credit commitments	8,143,000	(1,486,000)	7,357,000	453,000
Allowance for Unfunded Credit Commitments	28,972,000	13,019,000	28,972,000	13,019,000	11,158,000		$ 12,566,000
Unfunded Credit Commitments | Cumulative Effect, Period Of Adoption, Adjustment
Allowance for unfunded credit commitments
Allowance for Unfunded Credit Commitments	0	0	10,457,000	0	0
Allowance for Unfunded Credit Commitments					10,457,000		0
Commercial lending | Commercial and industrial (“C&I”)
Allowance for loan losses by portfolio segments
Allowance, beginning of period	362,629,000	189,757,000	238,376,000	189,117,000	189,117,000
Provision for credit losses	37,862,000	26,140,000	98,480,000	41,404,000
Gross charge-offs	(20,378,000)	(11,745,000)	(32,355,000)	(28,989,000)
Gross recoveries	602,000	1,713,000	2,177,000	3,964,000
Total net (charge-offs) recoveries	(19,776,000)	(10,032,000)	(30,178,000)	(25,025,000)
Foreign currency translation adjustments	8,000	(362,000)	(192,000)	7,000
Allowance, end of period	380,723,000	205,503,000	380,723,000	205,503,000	238,376,000		189,117,000
Allowance for unfunded credit commitments
Provision for (reversal of) credit losses on unfunded credit commitments	37,862,000	26,140,000	98,480,000	41,404,000
Commercial lending | Commercial and industrial (“C&I”) | PCD or PCI loans
Allowance for loan losses by portfolio segments
Allowance, beginning of period			0
Allowance, end of period					0
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
Allowance, end of period					74,237,000
Commercial lending | Commercial and industrial (“C&I”) | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses by portfolio segments
Allowance, beginning of period			312,613,000
Allowance, end of period					312,613,000
Commercial lending | Commercial real estate (“CRE”)
Allowance for loan losses by portfolio segments
Allowance, beginning of period	132,819,000	39,224,000	40,509,000	40,666,000	40,666,000
Provision for credit losses	43,315,000	(1,250,000)	54,750,000	(2,914,000)
Gross charge-offs	(320,000)	0	(1,274,000)	0
Gross recoveries	226,000	1,837,000	9,886,000	2,059,000
Total net (charge-offs) recoveries	(94,000)	1,837,000	8,612,000	2,059,000
Foreign currency translation adjustments	0		0	0
Allowance, end of period	176,040,000	39,811,000	176,040,000	39,811,000	40,509,000		40,666,000
Allowance for unfunded credit commitments
Provision for (reversal of) credit losses on unfunded credit commitments	43,315,000	(1,250,000)	54,750,000	(2,914,000)
Commercial lending | Commercial real estate (“CRE”) | PCD or PCI loans
Allowance for loan losses by portfolio segments
Allowance, beginning of period			0
Allowance, end of period					0
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
Allowance, end of period					72,169,000
Commercial lending | Commercial real estate (“CRE”) | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses by portfolio segments
Allowance, beginning of period			112,678,000
Allowance, end of period					112,678,000
Commercial lending | Real estate loan | Multifamily residential
Allowance for loan losses by portfolio segments
Allowance, beginning of period	16,530,000	19,169,000	22,826,000	19,885,000	19,885,000
Provision for credit losses	7,908,000	58,000	9,189,000	(939,000)
Gross charge-offs	0	0	0	0
Gross recoveries	620,000	53,000	1,155,000	334,000
Total net (charge-offs) recoveries	620,000	53,000	1,155,000	334,000
Foreign currency translation adjustments	0		0	0
Allowance, end of period	25,058,000	19,280,000	25,058,000	19,280,000	22,826,000		19,885,000
Allowance for unfunded credit commitments
Provision for (reversal of) credit losses on unfunded credit commitments	7,908,000	58,000	9,189,000	(939,000)
Commercial lending | Real estate loan | Multifamily residential | PCD or PCI loans
Allowance for loan losses by portfolio segments
Allowance, beginning of period			0
Allowance, end of period					0
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)
Allowance, end of period					(8,112,000)
Commercial lending | Real estate loan | Multifamily residential | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses by portfolio segments
Allowance, beginning of period			14,714,000
Allowance, end of period					14,714,000
Commercial lending | Construction and land
Allowance for loan losses by portfolio segments
Allowance, beginning of period	11,018,000	22,349,000	19,404,000	20,290,000	20,290,000
Provision for credit losses	7,526,000	173,000	9,008,000	2,169,000
Gross charge-offs	0	0	0	0
Gross recoveries	7,000	439,000	28,000	502,000
Total net (charge-offs) recoveries	7,000	439,000	28,000	502,000
Foreign currency translation adjustments	0		0	0
Allowance, end of period	18,551,000	22,961,000	18,551,000	22,961,000	19,404,000		20,290,000
Allowance for unfunded credit commitments
Provision for (reversal of) credit losses on unfunded credit commitments	7,526,000	173,000	9,008,000	2,169,000
Commercial lending | Construction and land | PCD or PCI loans
Allowance for loan losses by portfolio segments
Allowance, beginning of period			0
Allowance, end of period					0
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)
Allowance, end of period					(9,889,000)
Commercial lending | Construction and land | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses by portfolio segments
Allowance, beginning of period			9,515,000
Allowance, end of period					9,515,000
Consumer lending | Real estate loan | Single-family residential
Allowance for loan losses by portfolio segments
Allowance, beginning of period	26,822,000	35,759,000	28,527,000	31,340,000	31,340,000
Provision for credit losses	(1,667,000)	(3,068,000)	33,000	1,349,000
Gross charge-offs	0	0	0	0
Gross recoveries	159,000	72,000	424,000	74,000
Total net (charge-offs) recoveries	159,000	72,000	424,000	74,000
Foreign currency translation adjustments	0		0	0
Allowance, end of period	25,314,000	32,763,000	25,314,000	32,763,000	28,527,000		31,340,000
Allowance for unfunded credit commitments
Provision for (reversal of) credit losses on unfunded credit commitments	(1,667,000)	(3,068,000)	33,000	1,349,000
Consumer lending | Real estate loan | Single-family residential | PCD or PCI loans
Allowance for loan losses by portfolio segments
Allowance, beginning of period			0
Allowance, end of period					0
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)
Allowance, end of period					(3,670,000)
Consumer lending | Real estate loan | Single-family residential | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses by portfolio segments
Allowance, beginning of period			24,857,000
Allowance, end of period					24,857,000
Consumer lending | HELOCs
Allowance for loan losses by portfolio segments
Allowance, beginning of period	3,881,000	7,401,000	5,265,000	5,774,000	5,774,000
Provision for credit losses	205,000	(1,224,000)	617,000	401,000
Gross charge-offs	(221,000)	0	(221,000)	0
Gross recoveries	2,000	0	4,000	2,000
Total net (charge-offs) recoveries	(219,000)	0	(217,000)	2,000
Foreign currency translation adjustments	0		0	0
Allowance, end of period	3,867,000	6,177,000	3,867,000	6,177,000	5,265,000		5,774,000
Allowance for unfunded credit commitments
Provision for (reversal of) credit losses on unfunded credit commitments	205,000	(1,224,000)	617,000	401,000
Consumer lending | HELOCs | PCD or PCI loans
Allowance for loan losses by portfolio segments
Allowance, beginning of period			0
Allowance, end of period					0
Consumer lending | HELOCs | Cumulative Effect, Period Of Adoption, Adjustment
Allowance for loan losses by portfolio segments
Allowance, beginning of period			(1,798,000)
Allowance, end of period					(1,798,000)
Consumer lending | HELOCs | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses by portfolio segments
Allowance, beginning of period			3,467,000
Allowance, end of period					3,467,000
Consumer lending | Other consumer
Allowance for loan losses by portfolio segments
Allowance, beginning of period	3,304,000	4,235,000	3,380,000	4,250,000	4,250,000
Provision for credit losses	(849,000)	(98,000)	(3,121,000)	(99,000)
Gross charge-offs	(30,000)	(14,000)	(56,000)	(28,000)
Gross recoveries	93,000	7,000	94,000	7,000
Total net (charge-offs) recoveries	63,000	(7,000)	38,000	(21,000)
Foreign currency translation adjustments	0		0	0
Allowance, end of period	2,518,000	4,130,000	2,518,000	4,130,000	3,380,000		4,250,000
Allowance for unfunded credit commitments
Provision for (reversal of) credit losses on unfunded credit commitments	(849,000)	(98,000)	(3,121,000)	(99,000)
Consumer lending | Other consumer | PCD or PCI loans
Allowance for loan losses by portfolio segments
Allowance, beginning of period			0
Allowance, end of period					0
Consumer lending | Other consumer | Cumulative Effect, Period Of Adoption, Adjustment
Allowance for loan losses by portfolio segments
Allowance, beginning of period			2,221,000
Allowance, end of period					2,221,000
Consumer lending | Other consumer | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses by portfolio segments
Allowance, beginning of period			5,601,000
Allowance, end of period					5,601,000
Commercial and consumer lending
Allowance for loan losses by portfolio segments
Allowance, beginning of period	557,003,000	317,894,000	358,287,000	311,322,000	311,322,000
Provision for credit losses	94,300,000	20,731,000	168,956,000	41,371,000
Gross charge-offs	(20,949,000)	(11,759,000)	(33,906,000)	(29,017,000)
Gross recoveries	1,709,000	4,121,000	13,768,000	6,942,000
Total net (charge-offs) recoveries	(19,240,000)	(7,638,000)	(20,138,000)	(22,075,000)
Foreign currency translation adjustments	8,000	(362,000)	(192,000)	7,000
Allowance, end of period	632,071,000	330,625,000	632,071,000	330,625,000	358,287,000		$ 311,322,000
Allowance for unfunded credit commitments
Provision for (reversal of) credit losses on unfunded credit commitments	$ 94,300,000	$ 20,731,000	168,956,000	$ 41,371,000
Commercial and consumer lending | Cumulative Effect, Period Of Adoption, Adjustment
Allowance for loan losses by portfolio segments
Allowance, beginning of period			125,158,000
Allowance, end of period					125,158,000
Commercial and consumer lending | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses by portfolio segments
Allowance, beginning of period			$ 483,445,000
Allowance, end of period					$ 483,445,000

[1] Represents the impact of the adoption of ASU 2016-13, Financial Instruments - Credit Losses (Topic 326) in the first quarter of 2020. Refer to Note 2 — Current Accounting Developments and Summary of Significant Accounting Policies to the Consolidated Financial Statements in this Quarterly Report on Form 10-Q (“this Form 10-Q”) for additional information.

[2] Represents the impact of the adoption of Accounting Standards Update (“ASU”) 2016-02, Leases (Topic 842) and subsequent related ASUs in the first quarter of 2019.