Loans Receivable and Allowance for Credit Losses (Composition of Non-PCI and PCI Loans) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	$ 33,730,377	$ 32,385,189
Allowance for loan losses	(330,625)	(311,322)
Loans held-for-investment, net	33,399,752	32,073,867
Commercial lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	25,318,543	24,326,631
Commercial lending \| Commercial and industrial (“C&I”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	12,402,967	12,056,970
Commercial lending \| Commercial real estate (“CRE”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	9,868,433	9,449,835
Commercial lending \| Real estate loan \| Multifamily residential
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	2,372,345	2,281,032
Commercial lending \| Construction and land
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	674,798	538,794
Consumer lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	8,411,834	8,058,558
Consumer lending \| Real estate loan \| Single-family residential
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	6,494,882	6,036,454
Consumer lending \| HELOCs
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	1,575,150	1,690,834
Consumer lending \| Other consumer
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	341,802	331,270
Non-PCI Loans
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	33,459,510	32,077,166
Allowance for loan losses	(330,620)	(311,300)
Loans held-for-investment, net	33,128,890	31,765,866
Net deferred loan fees, unearned fees, unamortized premiums and unaccreted discounts	(43,800)	(48,900)
Non-PCI Loans \| Commercial lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	25,146,180	24,124,659
Non-PCI Loans \| Commercial lending \| Commercial and industrial (“C&I”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	12,401,090	12,054,818
Non-PCI Loans \| Commercial lending \| Commercial real estate (“CRE”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	9,722,582	9,284,583
Non-PCI Loans \| Commercial lending \| Real estate loan \| Multifamily residential
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	2,347,751	2,246,506
Non-PCI Loans \| Commercial lending \| Construction and land
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	674,757	538,752
Non-PCI Loans \| Consumer lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	8,313,330	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	6,403,628	5,939,258
Non-PCI Loans \| Consumer lending \| HELOCs
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	1,567,900	1,681,979
Non-PCI Loans \| Consumer lending \| Other consumer
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	341,802	331,270
PCI Loans
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	270,867	308,023
Allowance for loan losses	(5)	(22)
Loans held-for-investment, net	270,862	308,001
Discount related to ASC 310-30	18,900	22,200
PCI Loans \| Commercial lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	172,363	201,972
PCI Loans \| Commercial lending \| Commercial and industrial (“C&I”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	1,877	2,152
PCI Loans \| Commercial lending \| Commercial real estate (“CRE”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	145,851	165,252
PCI Loans \| Commercial lending \| Real estate loan \| Multifamily residential
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	24,594	34,526
PCI Loans \| Commercial lending \| Construction and land
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	41	42
PCI Loans \| Consumer lending
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	98,504	106,051
PCI Loans \| Consumer lending \| Real estate loan \| Single-family residential
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	91,254	97,196
PCI Loans \| Consumer lending \| HELOCs
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment	7,250	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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Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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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, before allowance for credit loss, of financing receivable.

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