Loans Receivable and Allowance for Credit Losses (Composition of Non-PCI and PCI Loans) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	$ 29,555,248	$ 28,975,718
Allowance for loan losses	(297,654)	(287,128)
Loans held-for-investment, net	29,257,594	28,688,590
Commercial lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	22,465,245	22,210,001
Commercial lending \| Commercial and industrial (“C&I”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	10,818,304	10,697,231
Commercial lending \| Commercial real estate (“CRE”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	9,022,746	8,936,897
Commercial lending \| Real estate loan \| Multifamily
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	1,954,855	1,916,176
Commercial lending \| Construction and land
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	669,340	659,697
Consumer lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	7,090,003	6,765,717
Consumer lending \| Real estate loan \| Single-family
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	4,930,580	4,646,289
Consumer lending \| Home equity lines of credit (“HELOCs”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	1,775,443	1,782,924
Consumer lending \| Other consumer
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	383,980	336,504
PCI Loans
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	452,403	482,287
Allowance for loan losses	(47)	(58)
Loans held-for-investment, net	452,356	482,229
Discount related to ASC 310-30	32,200	35,300
PCI Loans \| Commercial lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	327,260	350,902
PCI Loans \| Commercial lending \| Commercial and industrial (“C&I”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	11,042	11,795
PCI Loans \| Commercial lending \| Commercial real estate (“CRE”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	259,836	277,688
PCI Loans \| Commercial lending \| Real estate loan \| Multifamily
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	56,338	61,048
PCI Loans \| Commercial lending \| Construction and land
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	44	371
PCI Loans \| Consumer lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	125,143	131,385
PCI Loans \| Consumer lending \| Real estate loan \| Single-family
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	112,486	117,378
PCI Loans \| Consumer lending \| Home equity lines of credit (“HELOCs”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	12,657	14,007
PCI Loans \| Consumer lending \| Other consumer
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	0	0
Non-PCI Loans
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	29,102,845	28,493,431
Allowance for loan losses	(297,607)	(287,070)
Loans held-for-investment, net	28,805,238	28,206,361
Unearned fees, premiums and discounts, net	(36,600)	(34,000)
Non-PCI Loans \| Commercial lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	22,137,985	21,859,099
Non-PCI Loans \| Commercial lending \| Commercial and industrial (“C&I”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	10,807,262	10,685,436
Non-PCI Loans \| Commercial lending \| Commercial real estate (“CRE”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	8,762,910	8,659,209
Non-PCI Loans \| Commercial lending \| Real estate loan \| Multifamily
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	1,898,517	1,855,128
Non-PCI Loans \| Commercial lending \| Construction and land
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	669,296	659,326
Non-PCI Loans \| Consumer lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	6,964,860	6,634,332
Non-PCI Loans \| Consumer lending \| Real estate loan \| Single-family
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	4,818,094	4,528,911
Non-PCI Loans \| Consumer lending \| Home equity lines of credit (“HELOCs”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	1,762,786	1,768,917
Non-PCI Loans \| Consumer lending \| Other consumer
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	$ 383,980	$ 336,504

Financing Receivable, Discount

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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A valuation allowance for financing receivables that are expected to be uncollectible.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7)
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Amount representing an agreement for an unconditional promise by the maker to pay the entity (holder) a definite sum of money at a future date. Such amount may include accrued interest receivable in accordance with the terms of the note. The note also may contain provisions and related items including a discount or premium, payable on demand, secured, or unsecured, interest bearing or noninterest bearing, among a myriad of other features and characteristics. Excludes amounts related to receivables held-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.10(3))
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Amount of deferred fees paid by borrowers and unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield. Excludes amounts for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6378536&loc=d3e10092-111533

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