Loans Receivable and Allowance for Credit Losses (Credit Risk Ratings for Non-PCI Loans by Portfolio Segment) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	$ 30,230,379	$ 28,975,718
Commercial lending
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	22,769,945	22,210,001
Commercial lending | Commercial and industrial (“C&I”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	11,059,019	10,697,231
Commercial lending | Commercial real estate (“CRE”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	9,054,567	8,936,897
Commercial lending | Real estate loan | Multifamily
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	2,032,522	1,916,176
Commercial lending | Construction and land
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	623,837	659,697
Consumer lending
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	7,460,434	6,765,717
Consumer lending | Real estate loan | Single-family
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	5,316,895	4,646,289
Consumer lending | HELOCs
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,769,511	1,782,924
Consumer lending | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	374,028	336,504
Non-PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	29,846,694	28,493,431
Non-PCI Loans | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	29,297,366	27,878,020
Non-PCI Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	250,004	213,490
Non-PCI Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	298,033	381,039
Non-PCI Loans | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,291	20,882
Non-PCI Loans | Commercial lending
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	22,504,559	21,859,099
Non-PCI Loans | Commercial lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	21,983,211	21,308,550
Non-PCI Loans | Commercial lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	244,746	184,975
Non-PCI Loans | Commercial lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	275,311	344,692
Non-PCI Loans | Commercial lending | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,291	20,882
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	11,056,225	10,685,436
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	10,760,675	10,369,516
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	180,741	114,769
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	113,518	180,269
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,291	20,882
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	8,836,076	8,659,209
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	8,672,374	8,484,635
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	63,315	65,616
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	100,387	108,958
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,988,464	1,855,128
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,978,241	1,839,958
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	10,223	15,170
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
Non-PCI Loans | Commercial lending | Construction and land
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	623,794	659,326
Non-PCI Loans | Commercial lending | Construction and land | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	571,921	614,441
Non-PCI Loans | Commercial lending | Construction and land | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	690	4,590
Non-PCI Loans | Commercial lending | Construction and land | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	51,183	40,295
Non-PCI Loans | Commercial lending | Construction and land | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
Non-PCI Loans | Consumer lending
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	7,342,135	6,634,332
Non-PCI Loans | Consumer lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	7,314,155	6,569,470
Non-PCI Loans | Consumer lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	5,258	28,515
Non-PCI Loans | Consumer lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	22,722	36,347
Non-PCI Loans | Consumer lending | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
Non-PCI Loans | Consumer lending | Real estate loan | Single-family
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	5,210,014	4,528,911
Non-PCI Loans | Consumer lending | Real estate loan | Single-family | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	5,193,906	4,490,672
Non-PCI Loans | Consumer lending | Real estate loan | Single-family | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	4,063	16,504
Non-PCI Loans | Consumer lending | Real estate loan | Single-family | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	12,045	21,735
Non-PCI Loans | Consumer lending | Real estate loan | Single-family | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
Non-PCI Loans | Consumer lending | HELOCs
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,758,093	1,768,917
Non-PCI Loans | Consumer lending | HELOCs | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,748,719	1,744,903
Non-PCI Loans | Consumer lending | HELOCs | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,188	11,900
Non-PCI Loans | Consumer lending | HELOCs | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	8,186	12,114
Non-PCI Loans | Consumer lending | HELOCs | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
Non-PCI Loans | Consumer lending | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	374,028	336,504
Non-PCI Loans | Consumer lending | Other consumer | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	371,530	333,895
Non-PCI Loans | Consumer lending | Other consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	7	111
Non-PCI Loans | Consumer lending | Other consumer | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	2,491	2,498
Non-PCI Loans | Consumer lending | Other consumer | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	383,685	482,287
PCI Loans | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	349,007	432,628
PCI Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	5,297	2,131
PCI Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	29,381	47,528
PCI Loans | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	265,386	350,902
PCI Loans | Commercial lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	233,083	306,081
PCI Loans | Commercial lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	4,813	588
PCI Loans | Commercial lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	27,490	44,233
PCI Loans | Commercial lending | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Commercial and industrial (“C&I”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	2,794	11,795
PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	2,551	10,712
PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	57
PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	243	1,026
PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Commercial real estate (“CRE”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	218,491	277,688
PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	189,307	238,605
PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	4,813	531
PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	24,371	38,552
PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Real estate loan | Multifamily
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	44,058	61,048
PCI Loans | Commercial lending | Real estate loan | Multifamily | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	41,182	56,720
PCI Loans | Commercial lending | Real estate loan | Multifamily | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Real estate loan | Multifamily | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	2,876	4,328
PCI Loans | Commercial lending | Real estate loan | Multifamily | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Construction and land
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	43	371
PCI Loans | Commercial lending | Construction and land | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	43	44
PCI Loans | Commercial lending | Construction and land | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Construction and land | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	327
PCI Loans | Commercial lending | Construction and land | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Consumer lending
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	118,299	131,385
PCI Loans | Consumer lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	115,924	126,547
PCI Loans | Consumer lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	484	1,543
PCI Loans | Consumer lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,891	3,295
PCI Loans | Consumer lending | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Consumer lending | Real estate loan | Single-family
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	106,881	117,378
PCI Loans | Consumer lending | Real estate loan | Single-family | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	105,219	113,905
PCI Loans | Consumer lending | Real estate loan | Single-family | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	275	1,543
PCI Loans | Consumer lending | Real estate loan | Single-family | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,387	1,930
PCI Loans | Consumer lending | Real estate loan | Single-family | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Consumer lending | HELOCs
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	11,418	14,007
PCI Loans | Consumer lending | HELOCs | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	10,705	12,642
PCI Loans | Consumer lending | HELOCs | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	209	0
PCI Loans | Consumer lending | HELOCs | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	504	1,365
PCI Loans | Consumer lending | HELOCs | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Consumer lending | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	$ 0	$ 0