Loans Receivable and Allowance for Credit Losses (Credit Risk Ratings for Non-PCI Loans by Portfolio Segment) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	$ 28,975,718	$ 25,503,139
Commercial Lending
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	22,210,001	19,917,365
Commercial Lending | C&I
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	10,697,231	9,640,563
Commercial Lending | CRE
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	8,936,897	8,016,109
Commercial Lending | Residential loan | Multifamily
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	1,916,176	1,585,939
Commercial Lending | Construction and land
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	659,697	674,754
Consumer Lending
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	6,765,717	5,585,774
Consumer Lending | Residential loan | Single-family
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	4,646,289	3,509,779
Consumer Lending | HELOCs
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	1,782,924	1,760,776
Consumer Lending | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	336,504	315,219
Non-PCI impaired loans
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	28,493,431	24,860,694
Non-PCI impaired loans | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	27,878,020	24,177,983
Non-PCI impaired loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	213,490	212,927
Non-PCI impaired loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	381,039	464,609
Non-PCI impaired loans | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	20,882	5,167
Non-PCI impaired loans | Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	8
Non-PCI impaired loans | Commercial Lending
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	21,859,099	19,432,958
Non-PCI impaired loans | Commercial Lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	21,308,550	18,793,563
Non-PCI impaired loans | Commercial Lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	184,975	195,984
Non-PCI impaired loans | Commercial Lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	344,692	438,236
Non-PCI impaired loans | Commercial Lending | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	20,882	5,167
Non-PCI impaired loans | Commercial Lending | Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	8
Non-PCI impaired loans | Commercial Lending | C&I
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	10,685,436	9,602,176
Non-PCI impaired loans | Commercial Lending | C&I | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	10,369,516	9,194,701
Non-PCI impaired loans | Commercial Lending | C&I | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	114,769	164,711
Non-PCI impaired loans | Commercial Lending | C&I | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	180,269	237,599
Non-PCI impaired loans | Commercial Lending | C&I | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	20,882	5,157
Non-PCI impaired loans | Commercial Lending | C&I | Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	8
Non-PCI impaired loans | Commercial Lending | CRE
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	8,659,209	7,667,661
Non-PCI impaired loans | Commercial Lending | CRE | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	8,484,635	7,476,804
Non-PCI impaired loans | Commercial Lending | CRE | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	65,616	29,005
Non-PCI impaired loans | Commercial Lending | CRE | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	108,958	161,852
Non-PCI impaired loans | Commercial Lending | CRE | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
Non-PCI impaired loans | Commercial Lending | CRE | Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
Non-PCI impaired loans | Commercial Lending | Residential loan | Multifamily
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	1,855,128	1,490,285
Non-PCI impaired loans | Commercial Lending | Residential loan | Multifamily | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	1,839,958	1,462,522
Non-PCI impaired loans | Commercial Lending | Residential loan | Multifamily | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	2,268
Non-PCI impaired loans | Commercial Lending | Residential loan | Multifamily | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	15,170	25,495
Non-PCI impaired loans | Commercial Lending | Residential loan | Multifamily | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
Non-PCI impaired loans | Commercial Lending | Residential loan | Multifamily | Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
Non-PCI impaired loans | Commercial Lending | Construction and land
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	659,326	672,836
Non-PCI impaired loans | Commercial Lending | Construction and land | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	614,441	659,536
Non-PCI impaired loans | Commercial Lending | Construction and land | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	4,590	0
Non-PCI impaired loans | Commercial Lending | Construction and land | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	40,295	13,290
Non-PCI impaired loans | Commercial Lending | Construction and land | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	10
Non-PCI impaired loans | Commercial Lending | Construction and land | Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
Non-PCI impaired loans | Consumer Lending
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	6,634,332	5,427,736
Non-PCI impaired loans | Consumer Lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	6,569,470	5,384,420
Non-PCI impaired loans | Consumer Lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	28,515	16,943
Non-PCI impaired loans | Consumer Lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	36,347	26,373
Non-PCI impaired loans | Consumer Lending | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
Non-PCI impaired loans | Consumer Lending | Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
Non-PCI impaired loans | Consumer Lending | Residential loan | Single-family
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	4,528,911	3,370,669
Non-PCI impaired loans | Consumer Lending | Residential loan | Single-family | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	4,490,672	3,341,015
Non-PCI impaired loans | Consumer Lending | Residential loan | Single-family | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	16,504	10,179
Non-PCI impaired loans | Consumer Lending | Residential loan | Single-family | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	21,735	19,475
Non-PCI impaired loans | Consumer Lending | Residential loan | Single-family | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
Non-PCI impaired loans | Consumer Lending | Residential loan | Single-family | Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
Non-PCI impaired loans | Consumer Lending | HELOCs
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	1,768,917	1,741,852
Non-PCI impaired loans | Consumer Lending | HELOCs | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	1,744,903	1,728,254
Non-PCI impaired loans | Consumer Lending | HELOCs | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	11,900	6,717
Non-PCI impaired loans | Consumer Lending | HELOCs | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	12,114	6,881
Non-PCI impaired loans | Consumer Lending | HELOCs | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
Non-PCI impaired loans | Consumer Lending | HELOCs | Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
Non-PCI impaired loans | Consumer Lending | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	336,504	315,215
Non-PCI impaired loans | Consumer Lending | Other consumer | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	333,895	315,151
Non-PCI impaired loans | Consumer Lending | Other consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	111	47
Non-PCI impaired loans | Consumer Lending | Other consumer | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	2,498	17
Non-PCI impaired loans | Consumer Lending | Other consumer | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
Non-PCI impaired loans | Consumer Lending | Other consumer | Loss
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	482,287	642,445
PCI Loans | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	432,628	568,844
PCI Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	2,131	5,566
PCI Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	47,528	68,035
PCI Loans | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
PCI Loans | Loss
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	350,902	484,407
PCI Loans | Commercial Lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	306,081	415,166
PCI Loans | Commercial Lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	588	4,011
PCI Loans | Commercial Lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	44,233	65,230
PCI Loans | Commercial Lending | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
PCI Loans | Commercial Lending | Loss
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	11,795	38,387
PCI Loans | Commercial Lending | C&I | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	10,712	33,885
PCI Loans | Commercial Lending | C&I | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	57	772
PCI Loans | Commercial Lending | C&I | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	1,026	3,730
PCI Loans | Commercial Lending | C&I | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
PCI Loans | Commercial Lending | C&I | Loss
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	277,688	348,448
PCI Loans | Commercial Lending | CRE | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	238,605	293,529
PCI Loans | Commercial Lending | CRE | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	531	3,239
PCI Loans | Commercial Lending | CRE | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	38,552	51,680
PCI Loans | Commercial Lending | CRE | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
PCI Loans | Commercial Lending | CRE | Loss
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	61,048	95,654
PCI Loans | Commercial Lending | Residential loan | Multifamily | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	56,720	86,190
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	4,328	9,464
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 | Residential loan | Multifamily | Loss
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	371	1,918
PCI Loans | Commercial Lending | Construction and land | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	44	1,562
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	327	356
PCI Loans | Commercial Lending | Construction and land | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
PCI Loans | Commercial Lending | Construction and land | Loss
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	131,385	158,038
PCI Loans | Consumer Lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	126,547	153,678
PCI Loans | Consumer Lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	1,543	1,555
PCI Loans | Consumer Lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	3,295	2,805
PCI Loans | Consumer Lending | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
PCI Loans | Consumer Lending | Loss
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	117,378	139,110
PCI Loans | Consumer Lending | Residential loan | Single-family | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	113,905	136,245
PCI Loans | Consumer Lending | Residential loan | Single-family | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	1,543	1,239
PCI Loans | Consumer Lending | Residential loan | Single-family | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	1,930	1,626
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 | Residential loan | Single-family | Loss
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	14,007	18,924
PCI Loans | Consumer Lending | HELOCs | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	12,642	17,429
PCI Loans | Consumer Lending | HELOCs | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	316
PCI Loans | Consumer Lending | HELOCs | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	1,365	1,179
PCI Loans | Consumer Lending | HELOCs | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
PCI Loans | Consumer Lending | HELOCs | Loss
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	4
PCI Loans | Consumer Lending | Other consumer | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	4
PCI Loans | Consumer Lending | Other consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
PCI Loans | Consumer Lending | Other consumer | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
PCI Loans | Consumer Lending | Other consumer | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	0	0
PCI Loans | Consumer Lending | Other consumer | Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans held-for-investment	$ 0	$ 0