Loans Receivable and Allowance for Credit Losses (Credit Risk Ratings for Non-PCI Loans by Portfolio Segment) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	$ 31,210,185	$ 28,975,718
Commercial lending
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	23,474,977	22,210,001
Commercial lending | Commercial and industrial (“C&I”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	11,517,054	10,697,231
Commercial lending | Commercial real estate (“CRE”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	9,262,327	8,936,897
Commercial lending | Real estate loan | Multifamily residential
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	2,090,563	1,916,176
Commercial lending | Construction and land
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	605,033	659,697
Consumer lending
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	7,735,208	6,765,717
Consumer lending | Real estate loan | Single-family residential
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	5,684,587	4,646,289
Consumer lending | HELOCs
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,717,440	1,782,924
Consumer lending | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	333,181	336,504
Non-PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	30,865,161	28,493,431
Non-PCI Loans | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	30,248,885	27,878,020
Non-PCI Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	355,800	213,490
Non-PCI Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	253,107	381,039
Non-PCI Loans | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	7,369	20,882
Non-PCI Loans | Commercial lending
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	23,240,987	21,859,099
Non-PCI Loans | Commercial lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	22,647,842	21,308,550
Non-PCI Loans | Commercial lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	348,150	184,975
Non-PCI Loans | Commercial lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	237,626	344,692
Non-PCI Loans | Commercial lending | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	7,369	20,882
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	11,514,640	10,685,436
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	11,188,760	10,369,516
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	218,861	114,769
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	99,650	180,269
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	7,369	20,882
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	9,069,879	8,659,209
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	8,909,103	8,484,635
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	69,821	65,616
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	90,955	108,958
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	2,051,477	1,855,128
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	2,000,504	1,839,958
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	39,711	0
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	11,262	15,170
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	604,991	659,326
Non-PCI Loans | Commercial lending | Construction and land | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	549,475	614,441
Non-PCI Loans | Commercial lending | Construction and land | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	19,757	4,590
Non-PCI Loans | Commercial lending | Construction and land | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	35,759	40,295
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	7,624,174	6,634,332
Non-PCI Loans | Consumer lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	7,601,043	6,569,470
Non-PCI Loans | Consumer lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	7,650	28,515
Non-PCI Loans | Consumer lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	15,481	36,347
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	5,583,195	4,528,911
Non-PCI Loans | Consumer lending | Real estate loan | Single-family residential | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	5,575,271	4,490,672
Non-PCI Loans | Consumer lending | Real estate loan | Single-family residential | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	3,145	16,504
Non-PCI Loans | Consumer lending | Real estate loan | Single-family residential | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	4,779	21,735
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	1,707,798	1,768,917
Non-PCI Loans | Consumer lending | HELOCs | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,695,085	1,744,903
Non-PCI Loans | Consumer lending | HELOCs | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	4,502	11,900
Non-PCI Loans | Consumer lending | HELOCs | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	8,211	12,114
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	333,181	336,504
Non-PCI Loans | Consumer lending | Other consumer | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	330,687	333,895
Non-PCI Loans | Consumer lending | Other consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	3	111
Non-PCI Loans | Consumer lending | Other consumer | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	2,491	2,498
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	345,024	482,287
PCI Loans | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	318,243	432,628
PCI Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	524	2,131
PCI Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	26,257	47,528
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	233,990	350,902
PCI Loans | Commercial lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	208,458	306,081
PCI Loans | Commercial lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	133	588
PCI Loans | Commercial lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	25,399	44,233
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	2,414	11,795
PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	2,105	10,712
PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	133	57
PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	176	1,026
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	192,448	277,688
PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	169,809	238,605
PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	531
PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	22,639	38,552
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	39,086	61,048
PCI Loans | Commercial lending | Real estate loan | Multifamily residential | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	36,502	56,720
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	2,584	4,328
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	371
PCI Loans | Commercial lending | Construction and land | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	42	44
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	327
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	111,034	131,385
PCI Loans | Consumer lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	109,785	126,547
PCI Loans | Consumer lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	391	1,543
PCI Loans | Consumer lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	858	3,295
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	101,392	117,378
PCI Loans | Consumer lending | Real estate loan | Single-family residential | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	100,815	113,905
PCI Loans | Consumer lending | Real estate loan | Single-family residential | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	185	1,543
PCI Loans | Consumer lending | Real estate loan | Single-family residential | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	392	1,930
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	9,642	14,007
PCI Loans | Consumer lending | HELOCs | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	8,970	12,642
PCI Loans | Consumer lending | HELOCs | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	206	0
PCI Loans | Consumer lending | HELOCs | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	466	1,365
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