Loans Receivable and Allowance for Credit Losses (Credit Risk Ratings for Non-PCI Loans by Portfolio Segment) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	$ 32,863,286	$ 32,385,189
Commercial lending
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	24,595,114	24,326,631
Commercial lending | Commercial and industrial (“C&I”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	12,040,806	12,056,970
Commercial lending | Commercial real estate (“CRE”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	9,636,338	9,449,835
Commercial lending | Real estate loan | Multifamily residential
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	2,270,590	2,281,032
Commercial lending | Construction and land
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	647,380	538,794
Consumer lending
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	8,268,172	8,058,558
Consumer lending | Real estate loan | Single-family residential
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	6,309,331	6,036,454
Consumer lending | HELOCs
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,626,222	1,690,834
Consumer lending | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	332,619	331,270
Non-PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	32,572,958	32,077,166
Non-PCI Loans | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	31,764,713	31,413,557
Non-PCI Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	398,948	358,136
Non-PCI Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	386,732	295,058
Non-PCI Loans | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	22,565	10,415
Non-PCI Loans | Commercial lending
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	24,407,508	24,124,659
Non-PCI Loans | Commercial lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	23,654,634	23,489,906
Non-PCI Loans | Commercial lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	374,768	350,183
Non-PCI Loans | Commercial lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	355,541	274,155
Non-PCI Loans | Commercial lending | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	22,565	10,415
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	12,038,864	12,054,818
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	11,513,029	11,644,470
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	283,651	260,089
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	219,619	139,844
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	22,565	10,415
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	9,478,979	9,284,583
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	9,337,492	9,144,646
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	50,171	49,705
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	91,316	90,232
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily residential
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	2,242,327	2,246,506
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	2,210,481	2,215,573
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	20,900	20,551
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	10,946	10,382
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
Non-PCI Loans | Commercial lending | Construction and land
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	647,338	538,752
Non-PCI Loans | Commercial lending | Construction and land | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	593,632	485,217
Non-PCI Loans | Commercial lending | Construction and land | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	20,046	19,838
Non-PCI Loans | Commercial lending | Construction and land | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	33,660	33,697
Non-PCI Loans | Commercial lending | Construction and land | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
Non-PCI Loans | Consumer lending
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	8,165,450	7,952,507
Non-PCI Loans | Consumer lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	8,110,079	7,923,651
Non-PCI Loans | Consumer lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	24,180	7,953
Non-PCI Loans | Consumer lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	31,191	20,903
Non-PCI Loans | Consumer lending | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
Non-PCI Loans | Consumer lending | Real estate loan | Single-family residential
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	6,214,386	5,939,258
Non-PCI Loans | Consumer lending | Real estate loan | Single-family residential | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	6,192,411	5,925,584
Non-PCI Loans | Consumer lending | Real estate loan | Single-family residential | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	7,688	6,376
Non-PCI Loans | Consumer lending | Real estate loan | Single-family residential | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	14,287	7,298
Non-PCI Loans | Consumer lending | Real estate loan | Single-family residential | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
Non-PCI Loans | Consumer lending | HELOCs
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,618,445	1,681,979
Non-PCI Loans | Consumer lending | HELOCs | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,601,555	1,669,300
Non-PCI Loans | Consumer lending | HELOCs | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	2,492	1,576
Non-PCI Loans | Consumer lending | HELOCs | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	14,398	11,103
Non-PCI Loans | Consumer lending | HELOCs | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
Non-PCI Loans | Consumer lending | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	332,619	331,270
Non-PCI Loans | Consumer lending | Other consumer | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	316,113	328,767
Non-PCI Loans | Consumer lending | Other consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	14,000	1
Non-PCI Loans | Consumer lending | Other consumer | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	2,506	2,502
Non-PCI Loans | Consumer lending | Other consumer | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	290,328	308,023
PCI Loans | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	266,430	285,201
PCI Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,947	1,277
PCI Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	21,951	21,545
PCI Loans | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	187,606	201,972
PCI Loans | Commercial lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	166,013	181,098
PCI Loans | Commercial lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	719	0
PCI Loans | Commercial lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	20,874	20,874
PCI Loans | Commercial lending | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Commercial and industrial (“C&I”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,942	2,152
PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,942	1,996
PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	156
PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Commercial real estate (“CRE”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	157,359	165,252
PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	137,259	146,057
PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	719	0
PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	19,381	19,195
PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Real estate loan | Multifamily residential
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	28,263	34,526
PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	26,770	33,003
PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,493	1,523
PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Construction and land
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	42	42
PCI Loans | Commercial lending | Construction and land | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	42	42
PCI Loans | Commercial lending | Construction and land | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Construction and land | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Construction and land | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Consumer lending
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	102,722	106,051
PCI Loans | Consumer lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	100,417	104,103
PCI Loans | Consumer lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,228	1,277
PCI Loans | Consumer lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,077	671
PCI Loans | Consumer lending | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Consumer lending | Real estate loan | Single-family residential
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	94,945	97,196
PCI Loans | Consumer lending | Real estate loan | Single-family residential | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	93,375	95,789
PCI Loans | Consumer lending | Real estate loan | Single-family residential | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	772	1,021
PCI Loans | Consumer lending | Real estate loan | Single-family residential | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	798	386
PCI Loans | Consumer lending | Real estate loan | Single-family residential | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Consumer lending | HELOCs
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	7,777	8,855
PCI Loans | Consumer lending | HELOCs | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	7,042	8,314
PCI Loans | Consumer lending | HELOCs | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	456	256
PCI Loans | Consumer lending | HELOCs | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	279	285
PCI Loans | Consumer lending | HELOCs | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Consumer lending | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	$ 0	$ 0