Loans Receivable and Allowance for Credit Losses (Credit Risk Ratings for Non-PCI Loans by Portfolio Segment) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	$ 29,555,248	$ 28,975,718
Commercial lending
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	22,465,245	22,210,001
Commercial lending | Commercial and industrial (“C&I”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	10,818,304	10,697,231
Commercial lending | Commercial real estate (“CRE”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	9,022,746	8,936,897
Commercial lending | Real estate loan | Multifamily
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,954,855	1,916,176
Commercial lending | Construction and land
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	669,340	659,697
Consumer lending
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	7,090,003	6,765,717
Consumer lending | Real estate loan | Single-family
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	4,930,580	4,646,289
Consumer lending | Home equity lines of credit (“HELOCs”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,775,443	1,782,924
Consumer lending | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	383,980	336,504
Non-PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	29,102,845	28,493,431
Non-PCI Loans | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	28,516,465	27,878,020
Non-PCI Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	216,803	213,490
Non-PCI Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	341,659	381,039
Non-PCI Loans | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	27,918	20,882
Non-PCI Loans | Commercial lending
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	22,137,985	21,859,099
Non-PCI Loans | Commercial lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	21,578,108	21,308,550
Non-PCI Loans | Commercial lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	206,787	184,975
Non-PCI Loans | Commercial lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	325,172	344,692
Non-PCI Loans | Commercial lending | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	27,918	20,882
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	10,807,262	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	10,464,618	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	164,161	114,769
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	150,565	180,269
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	27,918	20,882
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	8,762,910	8,659,209
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	8,614,575	8,484,635
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	41,942	65,616
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	106,393	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
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,898,517	1,855,128
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,884,434	1,839,958
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	14,083	15,170
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily | 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	669,296	659,326
Non-PCI Loans | Commercial lending | Construction and land | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	614,481	614,441
Non-PCI Loans | Commercial lending | Construction and land | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	684	4,590
Non-PCI Loans | Commercial lending | Construction and land | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	54,131	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	6,964,860	6,634,332
Non-PCI Loans | Consumer lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	6,938,357	6,569,470
Non-PCI Loans | Consumer lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	10,016	28,515
Non-PCI Loans | Consumer lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	16,487	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
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	4,818,094	4,528,911
Non-PCI Loans | Consumer lending | Real estate loan | Single-family | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	4,803,472	4,490,672
Non-PCI Loans | Consumer lending | Real estate loan | Single-family | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	7,563	16,504
Non-PCI Loans | Consumer lending | Real estate loan | Single-family | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	7,059	21,735
Non-PCI Loans | Consumer lending | Real estate loan | Single-family | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
Non-PCI Loans | Consumer lending | Home equity lines of credit (“HELOCs”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,762,786	1,768,917
Non-PCI Loans | Consumer lending | Home equity lines of credit (“HELOCs”) | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	1,753,398	1,744,903
Non-PCI Loans | Consumer lending | Home equity lines of credit (“HELOCs”) | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	2,451	11,900
Non-PCI Loans | Consumer lending | Home equity lines of credit (“HELOCs”) | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	6,937	12,114
Non-PCI Loans | Consumer lending | Home equity lines of credit (“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	383,980	336,504
Non-PCI Loans | Consumer lending | Other consumer | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	381,487	333,895
Non-PCI Loans | Consumer lending | Other consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	2	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	452,403	482,287
PCI Loans | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	405,798	432,628
PCI Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	3,508	2,131
PCI Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	43,097	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	327,260	350,902
PCI Loans | Commercial lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	281,796	306,081
PCI Loans | Commercial lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	2,548	588
PCI Loans | Commercial lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	42,916	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	11,042	11,795
PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	10,071	10,712
PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	23	57
PCI Loans | Commercial lending | Commercial and industrial (“C&I”) | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	948	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	259,836	277,688
PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	219,255	238,605
PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	2,525	531
PCI Loans | Commercial lending | Commercial real estate (“CRE”) | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	38,056	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
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	56,338	61,048
PCI Loans | Commercial lending | Real estate loan | Multifamily | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	52,426	56,720
PCI Loans | Commercial lending | Real estate loan | Multifamily | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Commercial lending | Real estate loan | Multifamily | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	3,912	4,328
PCI Loans | Commercial lending | Real estate loan | Multifamily | 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	44	371
PCI Loans | Commercial lending | Construction and land | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	44	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	125,143	131,385
PCI Loans | Consumer lending | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	124,002	126,547
PCI Loans | Consumer lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	960	1,543
PCI Loans | Consumer lending | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	181	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
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	112,486	117,378
PCI Loans | Consumer lending | Real estate loan | Single-family | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	111,567	113,905
PCI Loans | Consumer lending | Real estate loan | Single-family | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	748	1,543
PCI Loans | Consumer lending | Real estate loan | Single-family | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	171	1,930
PCI Loans | Consumer lending | Real estate loan | Single-family | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	0	0
PCI Loans | Consumer lending | Home equity lines of credit (“HELOCs”)
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	12,657	14,007
PCI Loans | Consumer lending | Home equity lines of credit (“HELOCs”) | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	12,435	12,642
PCI Loans | Consumer lending | Home equity lines of credit (“HELOCs”) | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	212	0
PCI Loans | Consumer lending | Home equity lines of credit (“HELOCs”) | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans held-for-investment	10	1,365
PCI Loans | Consumer lending | Home equity lines of credit (“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