Loans Receivable and Allowance for Credit Losses (Credit Risk Ratings for Non-PCI Loans by Portfolio Segment) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	$ 33,730,377	$ 32,385,189
Commercial lending
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	25,318,543	24,326,631
Commercial lending | Commercial and industrial (“C&I”)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	12,402,967	12,056,970
Commercial lending | Commercial real estate (“CRE”)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	9,868,433	9,449,835
Commercial lending | Real estate loan | Multifamily residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	2,372,345	2,281,032
Commercial lending | Construction and land
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	674,798	538,794
Consumer lending
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	8,411,834	8,058,558
Consumer lending | Real estate loan | Single-family residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	6,494,882	6,036,454
Consumer lending | HELOCs
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	1,575,150	1,690,834
Consumer lending | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	341,802	331,270
Non-PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	33,459,510	32,077,166
Non-PCI Loans | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	32,520,960	31,413,557
Non-PCI Loans | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	528,768	358,136
Non-PCI Loans | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	397,894	295,058
Non-PCI Loans | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	11,888	10,415
Non-PCI Loans | Commercial lending
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	25,146,180	24,124,659
Non-PCI Loans | Commercial lending | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	24,260,235	23,489,906
Non-PCI Loans | Commercial lending | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	509,581	350,183
Non-PCI Loans | Commercial lending | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	364,476	274,155
Non-PCI Loans | Commercial lending | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	11,888	10,415
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	12,401,090	12,054,818
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	11,789,639	11,644,470
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	368,328	260,089
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	231,235	139,844
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	11,888	10,415
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	9,722,582	9,284,583
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	9,531,912	9,144,646
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	100,410	49,705
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	90,260	90,232
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	2,347,751	2,246,506
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	2,318,019	2,215,573
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	20,380	20,551
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	9,352	10,382
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
Non-PCI Loans | Commercial lending | Construction and land
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	674,757	538,752
Non-PCI Loans | Commercial lending | Construction and land | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	620,665	485,217
Non-PCI Loans | Commercial lending | Construction and land | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	20,463	19,838
Non-PCI Loans | Commercial lending | Construction and land | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	33,629	33,697
Non-PCI Loans | Commercial lending | Construction and land | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
Non-PCI Loans | Consumer lending
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	8,313,330	7,952,507
Non-PCI Loans | Consumer lending | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	8,260,725	7,923,651
Non-PCI Loans | Consumer lending | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	19,187	7,953
Non-PCI Loans | Consumer lending | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	33,418	20,903
Non-PCI Loans | Consumer lending | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
Non-PCI Loans | Consumer lending | Real estate loan | Single-family residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	6,403,628	5,939,258
Non-PCI Loans | Consumer lending | Real estate loan | Single-family residential | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	6,385,059	5,925,584
Non-PCI Loans | Consumer lending | Real estate loan | Single-family residential | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	1,471	6,376
Non-PCI Loans | Consumer lending | Real estate loan | Single-family residential | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	17,098	7,298
Non-PCI Loans | Consumer lending | Real estate loan | Single-family residential | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
Non-PCI Loans | Consumer lending | HELOCs
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	1,567,900	1,681,979
Non-PCI Loans | Consumer lending | HELOCs | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	1,550,377	1,669,300
Non-PCI Loans | Consumer lending | HELOCs | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	3,707	1,576
Non-PCI Loans | Consumer lending | HELOCs | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	13,816	11,103
Non-PCI Loans | Consumer lending | HELOCs | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
Non-PCI Loans | Consumer lending | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	341,802	331,270
Non-PCI Loans | Consumer lending | Other consumer | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	325,289	328,767
Non-PCI Loans | Consumer lending | Other consumer | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	14,009	1
Non-PCI Loans | Consumer lending | Other consumer | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	2,504	2,502
Non-PCI Loans | Consumer lending | Other consumer | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	270,867	308,023
PCI Loans | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	249,348	285,201
PCI Loans | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	770	1,277
PCI Loans | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	20,749	21,545
PCI Loans | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	172,363	201,972
PCI Loans | Commercial lending | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	152,857	181,098
PCI Loans | Commercial lending | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	6	0
PCI Loans | Commercial lending | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	19,500	20,874
PCI Loans | Commercial lending | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Commercial and industrial (“C&I”)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	1,877	2,152
PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	1,877	1,996
PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	156
PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Commercial real estate (“CRE”)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	145,851	165,252
PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	127,083	146,057
PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	6	0
PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	18,762	19,195
PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Real estate loan | Multifamily residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	24,594	34,526
PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	23,856	33,003
PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	738	1,523
PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Construction and land
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	41	42
PCI Loans | Commercial lending | Construction and land | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	41	42
PCI Loans | Commercial lending | Construction and land | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Construction and land | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Construction and land | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Consumer lending
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	98,504	106,051
PCI Loans | Consumer lending | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	96,491	104,103
PCI Loans | Consumer lending | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	764	1,277
PCI Loans | Consumer lending | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	1,249	671
PCI Loans | Consumer lending | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Consumer lending | Real estate loan | Single-family residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	91,254	97,196
PCI Loans | Consumer lending | Real estate loan | Single-family residential | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	89,623	95,789
PCI Loans | Consumer lending | Real estate loan | Single-family residential | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	764	1,021
PCI Loans | Consumer lending | Real estate loan | Single-family residential | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	867	386
PCI Loans | Consumer lending | Real estate loan | Single-family residential | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Consumer lending | HELOCs
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	7,250	8,855
PCI Loans | Consumer lending | HELOCs | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	6,868	8,314
PCI Loans | Consumer lending | HELOCs | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	256
PCI Loans | Consumer lending | HELOCs | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	382	285
PCI Loans | Consumer lending | HELOCs | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Consumer lending | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	$ 0	$ 0