Loans Receivable and Allowance for Credit Losses (Credit Risk Ratings for Non-PCI Loans by Portfolio Segment) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	$ 34,024,976	$ 32,385,189
Commercial lending
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	25,359,688	24,326,631
Commercial lending | Commercial and industrial (“C&I”)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	12,301,002	12,056,970
Commercial lending | Commercial real estate (“CRE”)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	9,749,583	9,260,199
Commercial lending | Real estate loan | Multifamily residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	2,589,203	2,470,668
Commercial lending | Construction and land
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	719,900	538,794
Consumer lending
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	8,665,288	8,058,558
Consumer lending | Real estate loan | Single-family residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	6,811,014	6,036,454
Consumer lending | HELOCs
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	1,540,121	1,690,834
Consumer lending | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	314,153	331,270
Non-PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	33,784,270	32,077,166
Non-PCI Loans | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	32,816,377	31,413,557
Non-PCI Loans | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	525,766	358,136
Non-PCI Loans | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	428,254	295,058
Non-PCI Loans | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	13,873	10,415
Non-PCI Loans | Commercial lending
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	25,211,110	24,124,659
Non-PCI Loans | Commercial lending | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	24,289,859	23,489,906
Non-PCI Loans | Commercial lending | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	501,028	350,183
Non-PCI Loans | Commercial lending | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	406,350	274,155
Non-PCI Loans | Commercial lending | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	13,873	10,415
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	12,299,163	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	11,632,851	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	390,052	260,089
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	262,387	139,844
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	13,873	10,415
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	9,627,330	9,097,165
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	9,454,709	8,957,228
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	90,583	49,705
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	82,038	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	2,564,758	2,433,924
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	2,535,702	2,402,991
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	20,393	20,551
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	8,663	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	719,859	538,752
Non-PCI Loans | Commercial lending | Construction and land | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	666,597	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	53,262	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	8,573,160	7,952,507
Non-PCI Loans | Consumer lending | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	8,526,518	7,923,651
Non-PCI Loans | Consumer lending | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	24,738	7,953
Non-PCI Loans | Consumer lending | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	21,904	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	6,725,574	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	6,708,317	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	7,773	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	9,484	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	1,533,433	1,681,979
Non-PCI Loans | Consumer lending | HELOCs | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	1,518,542	1,669,300
Non-PCI Loans | Consumer lending | HELOCs | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	4,966	1,576
Non-PCI Loans | Consumer lending | HELOCs | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	9,925	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	314,153	331,270
Non-PCI Loans | Consumer lending | Other consumer | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	299,659	328,767
Non-PCI Loans | Consumer lending | Other consumer | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	11,999	1
Non-PCI Loans | Consumer lending | Other consumer | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	2,495	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	240,706	308,023
PCI Loans | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	223,517	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	17,189	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	148,578	201,972
PCI Loans | Commercial lending | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	131,914	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	16,664	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	1,839	2,152
PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	1,839	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	122,253	163,034
PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	106,164	143,839
PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	16,089	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	24,445	36,744
PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	23,870	35,221
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	575	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	92,128	106,051
PCI Loans | Consumer lending | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	91,603	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	525	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	85,440	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	85,338	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	0	1,021
PCI Loans | Consumer lending | Real estate loan | Single-family residential | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	102	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	6,688	8,855
PCI Loans | Consumer lending | HELOCs | Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment	6,265	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	423	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