Loans Receivable and Allowance for Credit Losses (Credit Risk Ratings for Non-PCI and PCI Loans by Loan Type) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	$ 34,778,539	$ 32,385,189
Commercial Lending
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	25,914,252	24,326,631
Commercial Lending | C&I
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	12,150,931	12,056,970
Commercial Lending | CRE
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	10,278,448	9,260,199
Commercial Lending | Residential loan | Multifamily
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	2,856,374	2,470,668
Commercial Lending | Construction and land
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	628,499	538,794
Commercial Lending | Total CRE
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	13,763,321	12,269,661
Consumer Lending
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	8,864,287	8,058,558
Consumer Lending | Residential loan | Single-family
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	7,108,590	6,036,454
Consumer Lending | HELOCs
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	1,472,783	1,690,834
Consumer Lending | Total residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	8,581,373	7,727,288
Consumer Lending | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	282,914	331,270
Non-PCI loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	34,555,668	32,077,166
Non-PCI loans | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	33,582,886	31,413,557
Non-PCI loans | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	515,702	358,136
Non-PCI loans | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	440,105	295,058
Non-PCI loans | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	16,975	10,415
Non-PCI loans | Commercial Lending
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	25,777,039	24,124,659
Non-PCI loans | Commercial Lending | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	24,836,765	23,489,906
Non-PCI loans | Commercial Lending | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	510,632	350,183
Non-PCI loans | Commercial Lending | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	412,667	274,155
Non-PCI loans | Commercial Lending | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	16,975	10,415
Non-PCI loans | Commercial Lending | C&I
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	12,149,121	12,054,818
Non-PCI loans | Commercial Lending | C&I | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	11,423,094	11,644,470
Non-PCI loans | Commercial Lending | C&I | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	406,543	260,089
Non-PCI loans | Commercial Lending | C&I | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	302,509	139,844
Non-PCI loans | Commercial Lending | C&I | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	16,975	10,415
Non-PCI loans | Commercial Lending | CRE
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	10,165,247	9,097,165
Non-PCI loans | Commercial Lending | CRE | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	10,003,749	8,957,228
Non-PCI loans | Commercial Lending | CRE | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	83,683	49,705
Non-PCI loans | Commercial Lending | CRE | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	77,815	90,232
Non-PCI loans | Commercial Lending | CRE | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
Non-PCI loans | Commercial Lending | Residential loan | Multifamily
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	2,834,212	2,433,924
Non-PCI loans | Commercial Lending | Residential loan | Multifamily | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	2,806,475	2,402,991
Non-PCI loans | Commercial Lending | Residential loan | Multifamily | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	20,406	20,551
Non-PCI loans | Commercial Lending | Residential loan | Multifamily | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	7,331	10,382
Non-PCI loans | Commercial Lending | Residential loan | Multifamily | 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	628,459	538,752
Non-PCI loans | Commercial Lending | Construction and land | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	603,447	485,217
Non-PCI loans | Commercial Lending | Construction and land | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	19,838
Non-PCI loans | Commercial Lending | Construction and land | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	25,012	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 | Commercial Lending | Total CRE
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	13,627,918	12,069,841
Non-PCI loans | Commercial Lending | Total CRE | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	13,413,671	11,845,436
Non-PCI loans | Commercial Lending | Total CRE | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	104,089	90,094
Non-PCI loans | Commercial Lending | Total CRE | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	110,158	134,311
Non-PCI loans | Commercial Lending | Total CRE | 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	8,778,629	7,952,507
Non-PCI loans | Consumer Lending | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	8,746,121	7,923,651
Non-PCI loans | Consumer Lending | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	5,070	7,953
Non-PCI loans | Consumer Lending | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	27,438	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 | Residential loan | Single-family
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	7,028,979	5,939,258
Non-PCI loans | Consumer Lending | Residential loan | Single-family | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	7,012,522	5,925,584
Non-PCI loans | Consumer Lending | Residential loan | Single-family | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	2,278	6,376
Non-PCI loans | Consumer Lending | Residential loan | Single-family | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	14,179	7,298
Non-PCI loans | Consumer Lending | Residential loan | Single-family | 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	1,466,736	1,681,979
Non-PCI loans | Consumer Lending | HELOCs | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	1,453,207	1,669,300
Non-PCI loans | Consumer Lending | HELOCs | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	2,787	1,576
Non-PCI loans | Consumer Lending | HELOCs | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	10,742	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 | Total residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	8,495,715	7,621,237
Non-PCI loans | Consumer Lending | Total residential mortgage | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	8,465,729	7,594,884
Non-PCI loans | Consumer Lending | Total residential mortgage | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	5,065	7,952
Non-PCI loans | Consumer Lending | Total residential mortgage | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	24,921	18,401
Non-PCI loans | Consumer Lending | Total residential mortgage | 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	282,914	331,270
Non-PCI loans | Consumer Lending | Other consumer | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	280,392	328,767
Non-PCI loans | Consumer Lending | Other consumer | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	5	1
Non-PCI loans | Consumer Lending | Other consumer | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	2,517	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	222,871	308,023
PCI Loans | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	211,635	285,201
PCI Loans | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	1,277
PCI Loans | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	11,236	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	137,213	201,972
PCI Loans | Commercial Lending | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	126,269	181,098
PCI Loans | Commercial Lending | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial Lending | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	10,944	20,874
PCI Loans | Commercial Lending | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial Lending | C&I
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	1,810	2,152
PCI Loans | Commercial Lending | C&I | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	1,810	1,996
PCI Loans | Commercial Lending | C&I | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial Lending | C&I | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	156
PCI Loans | Commercial Lending | C&I | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial Lending | CRE
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	113,201	163,034
PCI Loans | Commercial Lending | CRE | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	102,257	143,839
PCI Loans | Commercial Lending | CRE | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial Lending | CRE | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	10,944	19,195
PCI Loans | Commercial Lending | CRE | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial Lending | Residential loan | Multifamily
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	22,162	36,744
PCI Loans | Commercial Lending | Residential loan | Multifamily | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	22,162	35,221
PCI Loans | Commercial Lending | Residential loan | Multifamily | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial Lending | Residential loan | Multifamily | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	1,523
PCI Loans | Commercial Lending | Residential loan | Multifamily | 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	40	42
PCI Loans | Commercial Lending | Construction and land | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	40	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 | Commercial Lending | Total CRE
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	135,403	199,820
PCI Loans | Commercial Lending | Total CRE | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	124,459	179,102
PCI Loans | Commercial Lending | Total CRE | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial Lending | Total CRE | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	10,944	20,718
PCI Loans | Commercial Lending | Total CRE | 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	85,658	106,051
PCI Loans | Consumer Lending | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	85,366	104,103
PCI Loans | Consumer Lending | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	1,277
PCI Loans | Consumer Lending | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	292	671
PCI Loans | Consumer Lending | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Consumer Lending | Residential loan | Single-family
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	79,611	97,196
PCI Loans | Consumer Lending | Residential loan | Single-family | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	79,517	95,789
PCI Loans | Consumer Lending | Residential loan | Single-family | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	1,021
PCI Loans | Consumer Lending | Residential loan | Single-family | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	94	386
PCI Loans | Consumer Lending | Residential loan | Single-family | 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	6,047	8,855
PCI Loans | Consumer Lending | HELOCs | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	5,849	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	198	285
PCI Loans | Consumer Lending | HELOCs | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Consumer Lending | Total residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	85,658	106,051
PCI Loans | Consumer Lending | Total residential mortgage | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	85,366	104,103
PCI Loans | Consumer Lending | Total residential mortgage | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	1,277
PCI Loans | Consumer Lending | Total residential mortgage | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	292	671
PCI Loans | Consumer Lending | Total residential mortgage | 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