Loans Receivable and Allowance for Credit Losses (Composition of Non-PCI and PCI Loans) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	$ 31,210,185	$ 28,975,718
Allowance for loan losses	(310,041)	(287,128)
Loans held-for-investment, net	30,900,144	28,688,590
Commercial lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	23,474,977	22,210,001
Commercial lending \| Commercial and industrial (“C&I”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	11,517,054	10,697,231
Commercial lending \| Commercial real estate (“CRE”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	9,262,327	8,936,897
Commercial lending \| Real estate loan \| Multifamily residential
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	2,090,563	1,916,176
Commercial lending \| Construction and land
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	605,033	659,697
Consumer lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	7,735,208	6,765,717
Consumer lending \| Real estate loan \| Single-family residential
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	5,684,587	4,646,289
Consumer lending \| HELOCs
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	1,717,440	1,782,924
Consumer lending \| Other consumer
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	333,181	336,504
PCI Loans
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	345,024	482,287
Allowance for loan losses	(31)	(58)
Loans held-for-investment, net	344,993	482,229
Discount related to ASC 310-30	24,500	35,300
PCI Loans \| Commercial lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	233,990	350,902
PCI Loans \| Commercial lending \| Commercial and industrial (“C&I”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	2,414	11,795
PCI Loans \| Commercial lending \| Commercial real estate (“CRE”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	192,448	277,688
PCI Loans \| Commercial lending \| Real estate loan \| Multifamily residential
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	39,086	61,048
PCI Loans \| Commercial lending \| Construction and land
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	42	371
PCI Loans \| Consumer lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	111,034	131,385
PCI Loans \| Consumer lending \| Real estate loan \| Single-family residential
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	101,392	117,378
PCI Loans \| Consumer lending \| HELOCs
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	9,642	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	30,865,161	28,493,431
Allowance for loan losses	(310,010)	(287,070)
Loans held-for-investment, net	30,555,151	28,206,361
Net deferred loan fees, unearned fees, unamortized premiums and unaccreted discounts	(42,400)	(34,000)
Non-PCI Loans \| Commercial lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	23,240,987	21,859,099
Non-PCI Loans \| Commercial lending \| Commercial and industrial (“C&I”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	11,514,640	10,685,436
Non-PCI Loans \| Commercial lending \| Commercial real estate (“CRE”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	9,069,879	8,659,209
Non-PCI Loans \| Commercial lending \| Real estate loan \| Multifamily residential
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	2,051,477	1,855,128
Non-PCI Loans \| Commercial lending \| Construction and land
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	604,991	659,326
Non-PCI Loans \| Consumer lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	7,624,174	6,634,332
Non-PCI Loans \| Consumer lending \| Real estate loan \| Single-family residential
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	5,583,195	4,528,911
Non-PCI Loans \| Consumer lending \| HELOCs
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	1,707,798	1,768,917
Non-PCI Loans \| Consumer lending \| Other consumer
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	$ 333,181	$ 336,504

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

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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.

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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.

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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.

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