Loans Receivable and Allowance for Credit Losses (Composition of Non-PCI and PCI Loans) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	$ 32,863,286	$ 32,385,189
Allowance for loan losses	(317,894)	(311,322)
Loans held-for-investment, net	32,545,392	32,073,867
Commercial lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	24,595,114	24,326,631
Commercial lending \| Commercial and industrial (“C&I”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	12,040,806	12,056,970
Commercial lending \| Commercial real estate (“CRE”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	9,636,338	9,449,835
Commercial lending \| Real estate loan \| Multifamily residential
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	2,270,590	2,281,032
Commercial lending \| Construction and land
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	647,380	538,794
Consumer lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	8,268,172	8,058,558
Consumer lending \| Real estate loan \| Single-family residential
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	6,309,331	6,036,454
Consumer lending \| HELOCs
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	1,626,222	1,690,834
Consumer lending \| Other consumer
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	332,619	331,270
Non-PCI Loans
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	32,572,958	32,077,166
Allowance for loan losses	(317,880)	(311,300)
Loans held-for-investment, net	32,255,078	31,765,866
Net deferred loan fees, unearned fees, unamortized premiums and unaccreted discounts	(46,000)	(48,900)
Non-PCI Loans \| Commercial lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	24,407,508	24,124,659
Non-PCI Loans \| Commercial lending \| Commercial and industrial (“C&I”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	12,038,864	12,054,818
Non-PCI Loans \| Commercial lending \| Commercial real estate (“CRE”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	9,478,979	9,284,583
Non-PCI Loans \| Commercial lending \| Real estate loan \| Multifamily residential
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	2,242,327	2,246,506
Non-PCI Loans \| Commercial lending \| Construction and land
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	647,338	538,752
Non-PCI Loans \| Consumer lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	8,165,450	7,952,507
Non-PCI Loans \| Consumer lending \| Real estate loan \| Single-family residential
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	6,214,386	5,939,258
Non-PCI Loans \| Consumer lending \| HELOCs
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	1,618,445	1,681,979
Non-PCI Loans \| Consumer lending \| Other consumer
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	332,619	331,270
PCI Loans
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	290,328	308,023
Allowance for loan losses	(14)	(22)
Loans held-for-investment, net	290,314	308,001
Discount related to ASC 310-30	20,400	22,200
PCI Loans \| Commercial lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	187,606	201,972
PCI Loans \| Commercial lending \| Commercial and industrial (“C&I”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	1,942	2,152
PCI Loans \| Commercial lending \| Commercial real estate (“CRE”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	157,359	165,252
PCI Loans \| Commercial lending \| Real estate loan \| Multifamily residential
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	28,263	34,526
PCI Loans \| Commercial lending \| Construction and land
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	42	42
PCI Loans \| Consumer lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	102,722	106,051
PCI Loans \| Consumer lending \| Real estate loan \| Single-family residential
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	94,945	97,196
PCI Loans \| Consumer lending \| HELOCs
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	7,777	8,855
PCI Loans \| Consumer lending \| Other consumer
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
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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