Loans Receivable and Allowance for Credit Losses (Aging Analysis on Non-PCI Loans) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Nonaccrual and Past Due Loans
Number of days beyond loan classified nonaccrual	90 days
Total loans	$ 30,230,379	$ 28,975,718
Commercial lending
Nonaccrual and Past Due Loans
Total loans	22,769,945	22,210,001
Commercial lending | Commercial and industrial (“C&I”)
Nonaccrual and Past Due Loans
Total loans	11,059,019	10,697,231
Commercial lending | Commercial real estate (“CRE”)
Nonaccrual and Past Due Loans
Total loans	9,054,567	8,936,897
Commercial lending | Real estate loan | Multifamily
Nonaccrual and Past Due Loans
Total loans	2,032,522	1,916,176
Commercial lending | Construction and land
Nonaccrual and Past Due Loans
Total loans	623,837	659,697
Consumer lending
Nonaccrual and Past Due Loans
Total loans	7,460,434	6,765,717
Consumer lending | Real estate loan | Single-family
Nonaccrual and Past Due Loans
Total loans	5,316,895	4,646,289
Consumer lending | HELOCs
Nonaccrual and Past Due Loans
Total loans	1,769,511	1,782,924
Consumer lending | Other consumer
Nonaccrual and Past Due Loans
Total loans	374,028	336,504
Non-PCI Loans
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	122,402	67,677
Total Nonaccrual Loans	102,823	114,309
Current Accruing Loans	29,621,469	28,311,445
Total loans	29,846,694	28,493,431
Non-PCI Loans | Accruing Loans 30-59 Days Past Due
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	115,987	57,551
Non-PCI Loans | Accruing Loans 60-89 Days Past Due
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	6,415	10,126
Non-PCI Loans | Nonaccrual Loans 90 or More Days Past Due
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	64,447	79,958
Non-PCI Loans | Nonaccrual Loans Less Than 90 Days Past Due
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	38,376	34,351
Non-PCI Loans | Commercial lending
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	91,792	40,544
Total Nonaccrual Loans	84,572	101,889
Current Accruing Loans	22,328,195	21,716,666
Total loans	22,504,559	21,859,099
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”)
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	86,965	31,046
Total Nonaccrual Loans	57,097	69,213
Current Accruing Loans	10,912,163	10,585,177
Total loans	11,056,225	10,685,436
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”)
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	2,913	3,880
Total Nonaccrual Loans	25,748	26,986
Current Accruing Loans	8,807,415	8,628,343
Total loans	8,836,076	8,659,209
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	1,914	4,860
Total Nonaccrual Loans	1,727	1,717
Current Accruing Loans	1,984,823	1,848,551
Total loans	1,988,464	1,855,128
Non-PCI Loans | Commercial lending | Construction and land
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	0	758
Total Nonaccrual Loans	0	3,973
Current Accruing Loans	623,794	654,595
Total loans	623,794	659,326
Non-PCI Loans | Commercial lending | Accruing Loans 30-59 Days Past Due
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	91,250	39,982
Non-PCI Loans | Commercial lending | Accruing Loans 30-59 Days Past Due | Commercial and industrial (“C&I”)
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	86,959	30,964
Non-PCI Loans | Commercial lending | Accruing Loans 30-59 Days Past Due | Commercial real estate (“CRE”)
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	2,913	3,414
Non-PCI Loans | Commercial lending | Accruing Loans 30-59 Days Past Due | Real estate loan | Multifamily
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	1,378	4,846
Non-PCI Loans | Commercial lending | Accruing Loans 30-59 Days Past Due | Construction and land
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	0	758
Non-PCI Loans | Commercial lending | Accruing Loans 60-89 Days Past Due
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	542	562
Non-PCI Loans | Commercial lending | Accruing Loans 60-89 Days Past Due | Commercial and industrial (“C&I”)
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	6	82
Non-PCI Loans | Commercial lending | Accruing Loans 60-89 Days Past Due | Commercial real estate (“CRE”)
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	0	466
Non-PCI Loans | Commercial lending | Accruing Loans 60-89 Days Past Due | Real estate loan | Multifamily
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	536	14
Non-PCI Loans | Commercial lending | Accruing Loans 60-89 Days Past Due | Construction and land
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	0	0
Non-PCI Loans | Commercial lending | Nonaccrual Loans 90 or More Days Past Due
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	48,503	67,633
Non-PCI Loans | Commercial lending | Nonaccrual Loans 90 or More Days Past Due | Commercial and industrial (“C&I”)
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	28,606	41,805
Non-PCI Loans | Commercial lending | Nonaccrual Loans 90 or More Days Past Due | Commercial real estate (“CRE”)
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	19,897	21,556
Non-PCI Loans | Commercial lending | Nonaccrual Loans 90 or More Days Past Due | Real estate loan | Multifamily
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	0	299
Non-PCI Loans | Commercial lending | Nonaccrual Loans 90 or More Days Past Due | Construction and land
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	0	3,973
Non-PCI Loans | Commercial lending | Nonaccrual Loans Less Than 90 Days Past Due
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	36,069	34,256
Non-PCI Loans | Commercial lending | Nonaccrual Loans Less Than 90 Days Past Due | Commercial and industrial (“C&I”)
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	28,491	27,408
Non-PCI Loans | Commercial lending | Nonaccrual Loans Less Than 90 Days Past Due | Commercial real estate (“CRE”)
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	5,851	5,430
Non-PCI Loans | Commercial lending | Nonaccrual Loans Less Than 90 Days Past Due | Real estate loan | Multifamily
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	1,727	1,418
Non-PCI Loans | Commercial lending | Nonaccrual Loans Less Than 90 Days Past Due | Construction and land
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	0	0
Non-PCI Loans | Consumer lending
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	30,610	27,133
Total Nonaccrual Loans	18,251	12,420
Current Accruing Loans	7,293,274	6,594,779
Total loans	7,342,135	6,634,332
Non-PCI Loans | Consumer lending | Real estate loan | Single-family
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	23,377	18,624
Total Nonaccrual Loans	7,625	5,923
Current Accruing Loans	5,179,012	4,504,364
Total loans	5,210,014	4,528,911
Non-PCI Loans | Consumer lending | HELOCs
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	7,206	8,472
Total Nonaccrual Loans	8,135	4,006
Current Accruing Loans	1,742,752	1,756,439
Total loans	1,758,093	1,768,917
Non-PCI Loans | Consumer lending | Other consumer
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	27	37
Total Nonaccrual Loans	2,491	2,491
Current Accruing Loans	371,510	333,976
Total loans	374,028	336,504
Non-PCI Loans | Consumer lending | Accruing Loans 30-59 Days Past Due
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	24,737	17,569
Non-PCI Loans | Consumer lending | Accruing Loans 30-59 Days Past Due | Real estate loan | Single-family
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	18,699	13,269
Non-PCI Loans | Consumer lending | Accruing Loans 30-59 Days Past Due | HELOCs
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	6,018	4,286
Non-PCI Loans | Consumer lending | Accruing Loans 30-59 Days Past Due | Other consumer
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	20	14
Non-PCI Loans | Consumer lending | Accruing Loans 60-89 Days Past Due
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	5,873	9,564
Non-PCI Loans | Consumer lending | Accruing Loans 60-89 Days Past Due | Real estate loan | Single-family
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	4,678	5,355
Non-PCI Loans | Consumer lending | Accruing Loans 60-89 Days Past Due | HELOCs
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	1,188	4,186
Non-PCI Loans | Consumer lending | Accruing Loans 60-89 Days Past Due | Other consumer
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	7	23
Non-PCI Loans | Consumer lending | Nonaccrual Loans 90 or More Days Past Due
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	15,944	12,325
Non-PCI Loans | Consumer lending | Nonaccrual Loans 90 or More Days Past Due | Real estate loan | Single-family
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	7,207	5,917
Non-PCI Loans | Consumer lending | Nonaccrual Loans 90 or More Days Past Due | HELOCs
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	6,246	3,917
Non-PCI Loans | Consumer lending | Nonaccrual Loans 90 or More Days Past Due | Other consumer
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	2,491	2,491
Non-PCI Loans | Consumer lending | Nonaccrual Loans Less Than 90 Days Past Due
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	2,307	95
Non-PCI Loans | Consumer lending | Nonaccrual Loans Less Than 90 Days Past Due | Real estate loan | Single-family
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	418	6
Non-PCI Loans | Consumer lending | Nonaccrual Loans Less Than 90 Days Past Due | HELOCs
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	1,889	89
Non-PCI Loans | Consumer lending | Nonaccrual Loans Less Than 90 Days Past Due | Other consumer
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	$ 0	$ 0