Loans Receivable and Allowance for Credit Losses (Composition of Non-PCI and PCI Loans) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	$ 32,385,189	$ 28,975,718
Allowance for loan losses	(311,322)	(287,128)
Loans held-for-investment, net	32,073,867	28,688,590
Commercial Lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	24,326,631	22,210,001
Commercial Lending \| C&I
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	12,056,970	10,697,231
Commercial Lending \| CRE
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	9,449,835	8,936,897
Commercial Lending \| Residential loan \| Multifamily
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	2,281,032	1,916,176
Commercial Lending \| Construction and land
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	538,794	659,697
Consumer Lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	8,058,558	6,765,717
Consumer Lending \| Residential loan \| Single-family
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	6,036,454	4,646,289
Consumer Lending \| HELOCs
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	1,690,834	1,782,924
Consumer Lending \| Other consumer
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	331,270	336,504
Non-PCI loans
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	32,077,166	28,493,431
Allowance for loan losses	(311,300)	(287,070)
Loans held-for-investment, net	31,765,866	28,206,361
Deferred loan fees, unearned fees, unamortized premiums and unaccreted discounts	(48,900)	(34,000)
Non-PCI loans \| Commercial Lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	24,124,659	21,859,099
Non-PCI loans \| Commercial Lending \| C&I
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	12,054,818	10,685,436
Non-PCI loans \| Commercial Lending \| CRE
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	9,284,583	8,659,209
Non-PCI loans \| Commercial Lending \| Residential loan \| Multifamily
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	2,246,506	1,855,128
Non-PCI loans \| Commercial Lending \| Construction and land
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	538,752	659,326
Non-PCI loans \| Consumer Lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	7,952,507	6,634,332
Non-PCI loans \| Consumer Lending \| Residential loan \| Single-family
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	5,939,258	4,528,911
Non-PCI loans \| Consumer Lending \| HELOCs
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	1,681,979	1,768,917
Non-PCI loans \| Consumer Lending \| Other consumer
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	331,270	336,504
PCI Loans
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	308,023	482,287
Allowance for loan losses	(22)	(58)
Loans held-for-investment, net	308,001	482,229
Discount related to ASC 310-30	22,200	35,300
PCI Loans \| Commercial Lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	201,972	350,902
PCI Loans \| Commercial Lending \| C&I
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	2,152	11,795
PCI Loans \| Commercial Lending \| CRE
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	165,252	277,688
PCI Loans \| Commercial Lending \| Residential loan \| Multifamily
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	34,526	61,048
PCI Loans \| Commercial Lending \| Construction and land
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	42	371
PCI Loans \| Consumer Lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	106,051	131,385
PCI Loans \| Consumer Lending \| Residential loan \| Single-family
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	97,196	117,378
PCI Loans \| Consumer Lending \| HELOCs
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	8,855	14,007
PCI Loans \| Consumer Lending \| Other consumer
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Total loans held-for-investment	$ 0	$ 0

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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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