Loans Receivable and Allowance for Credit Losses (Composition of Non-PCI and PCI Loans) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	$ 30,230,379	$ 28,975,718
Allowance for loan losses	(301,550)	(287,128)
Loans held-for-investment, net	29,928,829	28,688,590
Commercial lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	22,769,945	22,210,001
Commercial lending \| Commercial and industrial (“C&I”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	11,059,019	10,697,231
Commercial lending \| Commercial real estate (“CRE”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	9,054,567	8,936,897
Commercial lending \| Real estate loan \| Multifamily
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	2,032,522	1,916,176
Commercial lending \| Construction and land
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	623,837	659,697
Consumer lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	7,460,434	6,765,717
Consumer lending \| Real estate loan \| Single-family
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	5,316,895	4,646,289
Consumer lending \| HELOCs
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	1,769,511	1,782,924
Consumer lending \| Other consumer
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	374,028	336,504
PCI Loans
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	383,685	482,287
Allowance for loan losses	(39)	(58)
Loans held-for-investment, net	383,646	482,229
Discount related to ASC 310-30	26,800	35,300
PCI Loans \| Commercial lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	265,386	350,902
PCI Loans \| Commercial lending \| Commercial and industrial (“C&I”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	2,794	11,795
PCI Loans \| Commercial lending \| Commercial real estate (“CRE”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	218,491	277,688
PCI Loans \| Commercial lending \| Real estate loan \| Multifamily
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	44,058	61,048
PCI Loans \| Commercial lending \| Construction and land
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	43	371
PCI Loans \| Consumer lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	118,299	131,385
PCI Loans \| Consumer lending \| Real estate loan \| Single-family
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	106,881	117,378
PCI Loans \| Consumer lending \| HELOCs
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	11,418	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	29,846,694	28,493,431
Allowance for loan losses	(301,511)	(287,070)
Loans held-for-investment, net	29,545,183	28,206,361
Net deferred loan fees, unearned fees, unamortized premiums and unaccreted discounts	(40,400)	(34,000)
Non-PCI Loans \| Commercial lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	22,504,559	21,859,099
Non-PCI Loans \| Commercial lending \| Commercial and industrial (“C&I”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	11,056,225	10,685,436
Non-PCI Loans \| Commercial lending \| Commercial real estate (“CRE”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	8,836,076	8,659,209
Non-PCI Loans \| Commercial lending \| Real estate loan \| Multifamily
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	1,988,464	1,855,128
Non-PCI Loans \| Commercial lending \| Construction and land
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	623,794	659,326
Non-PCI Loans \| Consumer lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	7,342,135	6,634,332
Non-PCI Loans \| Consumer lending \| Real estate loan \| Single-family
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	5,210,014	4,528,911
Non-PCI Loans \| Consumer lending \| HELOCs
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	1,758,093	1,768,917
Non-PCI Loans \| Consumer lending \| Other consumer
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	$ 374,028	$ 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
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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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