Loans Receivable and Allowance for Credit Losses (Credit Risk Ratings for Non-PCI Loans by Portfolio Segment) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	$ 32,385,189	$ 28,975,718
Commercial Lending
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	24,326,631	22,210,001
Commercial Lending | C&I
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	12,056,970	10,697,231
Commercial Lending | CRE
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	9,449,835	8,936,897
Commercial Lending | Residential loan | Multifamily
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	2,281,032	1,916,176
Commercial Lending | Construction and land
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	538,794	659,697
Consumer Lending
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	8,058,558	6,765,717
Consumer Lending | Residential loan | Single-family
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	6,036,454	4,646,289
Consumer Lending | HELOCs
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	1,690,834	1,782,924
Consumer Lending | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	331,270	336,504
Non-PCI loans
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	32,077,166	28,493,431
Non-PCI loans | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	31,413,557	27,878,020
Non-PCI loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	358,136	213,490
Non-PCI loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	295,058	381,039
Non-PCI loans | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	10,415	20,882
Non-PCI loans | Commercial Lending
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	24,124,659	21,859,099
Non-PCI loans | Commercial Lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	23,489,906	21,308,550
Non-PCI loans | Commercial Lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	350,183	184,975
Non-PCI loans | Commercial Lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	274,155	344,692
Non-PCI loans | Commercial Lending | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	10,415	20,882
Non-PCI loans | Commercial Lending | C&I
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	12,054,818	10,685,436
Non-PCI loans | Commercial Lending | C&I | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	11,644,470	10,369,516
Non-PCI loans | Commercial Lending | C&I | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	260,089	114,769
Non-PCI loans | Commercial Lending | C&I | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	139,844	180,269
Non-PCI loans | Commercial Lending | C&I | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	10,415	20,882
Non-PCI loans | Commercial Lending | CRE
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	9,284,583	8,659,209
Non-PCI loans | Commercial Lending | CRE | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	9,144,646	8,484,635
Non-PCI loans | Commercial Lending | CRE | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	49,705	65,616
Non-PCI loans | Commercial Lending | CRE | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	90,232	108,958
Non-PCI loans | Commercial Lending | CRE | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
Non-PCI loans | Commercial Lending | Residential loan | Multifamily
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	2,246,506	1,855,128
Non-PCI loans | Commercial Lending | Residential loan | Multifamily | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	2,215,573	1,839,958
Non-PCI loans | Commercial Lending | Residential loan | Multifamily | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	20,551	0
Non-PCI loans | Commercial Lending | Residential loan | Multifamily | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	10,382	15,170
Non-PCI loans | Commercial Lending | Residential loan | Multifamily | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
Non-PCI loans | Commercial Lending | Construction and land
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	538,752	659,326
Non-PCI loans | Commercial Lending | Construction and land | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	485,217	614,441
Non-PCI loans | Commercial Lending | Construction and land | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	19,838	4,590
Non-PCI loans | Commercial Lending | Construction and land | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	33,697	40,295
Non-PCI loans | Commercial Lending | Construction and land | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
Non-PCI loans | Consumer Lending
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	7,952,507	6,634,332
Non-PCI loans | Consumer Lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	7,923,651	6,569,470
Non-PCI loans | Consumer Lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	7,953	28,515
Non-PCI loans | Consumer Lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	20,903	36,347
Non-PCI loans | Consumer Lending | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
Non-PCI loans | Consumer Lending | Residential loan | Single-family
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	5,939,258	4,528,911
Non-PCI loans | Consumer Lending | Residential loan | Single-family | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	5,925,584	4,490,672
Non-PCI loans | Consumer Lending | Residential loan | Single-family | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	6,376	16,504
Non-PCI loans | Consumer Lending | Residential loan | Single-family | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	7,298	21,735
Non-PCI loans | Consumer Lending | Residential loan | Single-family | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
Non-PCI loans | Consumer Lending | HELOCs
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	1,681,979	1,768,917
Non-PCI loans | Consumer Lending | HELOCs | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	1,669,300	1,744,903
Non-PCI loans | Consumer Lending | HELOCs | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	1,576	11,900
Non-PCI loans | Consumer Lending | HELOCs | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	11,103	12,114
Non-PCI loans | Consumer Lending | HELOCs | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
Non-PCI loans | Consumer Lending | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	331,270	336,504
Non-PCI loans | Consumer Lending | Other consumer | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	328,767	333,895
Non-PCI loans | Consumer Lending | Other consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	1	111
Non-PCI loans | Consumer Lending | Other consumer | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	2,502	2,498
Non-PCI loans | Consumer Lending | Other consumer | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	308,023	482,287
PCI Loans | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	285,201	432,628
PCI Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	1,277	2,131
PCI Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	21,545	47,528
PCI Loans | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
PCI Loans | Commercial Lending
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	201,972	350,902
PCI Loans | Commercial Lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	181,098	306,081
PCI Loans | Commercial Lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	588
PCI Loans | Commercial Lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	20,874	44,233
PCI Loans | Commercial Lending | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
PCI Loans | Commercial Lending | C&I
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	2,152	11,795
PCI Loans | Commercial Lending | C&I | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	1,996	10,712
PCI Loans | Commercial Lending | C&I | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	57
PCI Loans | Commercial Lending | C&I | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	156	1,026
PCI Loans | Commercial Lending | C&I | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
PCI Loans | Commercial Lending | CRE
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	165,252	277,688
PCI Loans | Commercial Lending | CRE | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	146,057	238,605
PCI Loans | Commercial Lending | CRE | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	531
PCI Loans | Commercial Lending | CRE | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	19,195	38,552
PCI Loans | Commercial Lending | CRE | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
PCI Loans | Commercial Lending | Residential loan | Multifamily
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	34,526	61,048
PCI Loans | Commercial Lending | Residential loan | Multifamily | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	33,003	56,720
PCI Loans | Commercial Lending | Residential loan | Multifamily | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
PCI Loans | Commercial Lending | Residential loan | Multifamily | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	1,523	4,328
PCI Loans | Commercial Lending | Residential loan | Multifamily | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
PCI Loans | Commercial Lending | Construction and land
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	42	371
PCI Loans | Commercial Lending | Construction and land | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	42	44
PCI Loans | Commercial Lending | Construction and land | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
PCI Loans | Commercial Lending | Construction and land | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	327
PCI Loans | Commercial Lending | Construction and land | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
PCI Loans | Consumer Lending
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	106,051	131,385
PCI Loans | Consumer Lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	104,103	126,547
PCI Loans | Consumer Lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	1,277	1,543
PCI Loans | Consumer Lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	671	3,295
PCI Loans | Consumer Lending | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
PCI Loans | Consumer Lending | Residential loan | Single-family
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	97,196	117,378
PCI Loans | Consumer Lending | Residential loan | Single-family | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	95,789	113,905
PCI Loans | Consumer Lending | Residential loan | Single-family | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	1,021	1,543
PCI Loans | Consumer Lending | Residential loan | Single-family | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	386	1,930
PCI Loans | Consumer Lending | Residential loan | Single-family | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
PCI Loans | Consumer Lending | HELOCs
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	8,855	14,007
PCI Loans | Consumer Lending | HELOCs | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	8,314	12,642
PCI Loans | Consumer Lending | HELOCs | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	256	0
PCI Loans | Consumer Lending | HELOCs | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	285	1,365
PCI Loans | Consumer Lending | HELOCs | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
PCI Loans | Consumer Lending | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	$ 0	$ 0