Loans Receivable and Allowance for Credit Losses (Summary of Activities in Allowance for Loan Losses) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Allowance for loan losses
Beginning balance	$ 287,128
Ending balance	297,654	$ 263,094
Commercial lending \| Commercial and industrial (“C&I”)
Allowance for loan losses
Beginning balance	163,058
Ending balance	169,695
Commercial lending \| Commercial real estate (“CRE”)
Allowance for loan losses
Beginning balance	41,237
Ending balance	39,718
Commercial lending \| Real estate loan \| Multifamily
Allowance for loan losses
Beginning balance	19,109
Ending balance	18,499
Commercial lending \| Construction and land
Allowance for loan losses
Beginning balance	26,881
Ending balance	32,220
Consumer lending \| Real estate loan \| Single-family
Allowance for loan losses
Beginning balance	26,362
Ending balance	25,957
Consumer lending \| Home equity lines of credit (“HELOCs”)
Allowance for loan losses
Beginning balance	7,354
Ending balance	7,041
Consumer lending \| Other consumer
Allowance for loan losses
Beginning balance	3,127
Ending balance	4,524
Non-PCI Loans
Allowance for loan losses
Beginning balance	287,070	260,402
(Reversal of) provision for loan losses	19,933	8,046
Charge-offs	(18,463)	(7,209)
Recoveries	9,067	1,768
Net recoveries (charge-offs)	(9,396)	(5,441)
Ending balance	297,607	263,007
Non-PCI Loans \| Commercial lending \| Commercial and industrial (“C&I”)
Allowance for loan losses
Charge-offs	(18,445)	(7,057)
Recoveries	7,687	455
Non-PCI Loans \| Commercial lending \| Commercial real estate (“CRE”)
Allowance for loan losses
Recoveries	427	569
Non-PCI Loans \| Commercial lending \| Real estate loan \| Multifamily
Allowance for loan losses
Recoveries	333	567
Non-PCI Loans \| Commercial lending \| Construction and land
Allowance for loan losses
Charge-offs	0	(148)
Recoveries	435	24
Non-PCI Loans \| Consumer lending \| Real estate loan \| Single-family
Allowance for loan losses
Charge-offs	(1)	0
Recoveries	184	11
Non-PCI Loans \| Consumer lending \| Home equity lines of credit (“HELOCs”)
Allowance for loan losses
Recoveries	0	24
Non-PCI Loans \| Consumer lending \| Other consumer
Allowance for loan losses
Charge-offs	17	(4)
Recoveries	1	118
PCI Loans
Allowance for loan losses
Beginning balance	58	118
(Reversal of) provision for loan losses	(11)	(31)
Ending balance	47	$ 87
PCI Loans \| Commercial lending \| Commercial and industrial (“C&I”)
Allowance for loan losses
Beginning balance	0
Ending balance	0
PCI Loans \| Commercial lending \| Commercial real estate (“CRE”)
Allowance for loan losses
Beginning balance	58
Ending balance	47
PCI Loans \| Commercial lending \| Real estate loan \| Multifamily
Allowance for loan losses
Beginning balance	0
Ending balance	0
PCI Loans \| Commercial lending \| Construction and land
Allowance for loan losses
Beginning balance	0
Ending balance	0
PCI Loans \| Consumer lending \| Real estate loan \| Single-family
Allowance for loan losses
Beginning balance	0
Ending balance	0
PCI Loans \| Consumer lending \| Home equity lines of credit (“HELOCs”)
Allowance for loan losses
Beginning balance	0
Ending balance	0
PCI Loans \| Consumer lending \| Other consumer
Allowance for loan losses
Beginning balance	0
Ending balance	$ 0

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

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Amount, after recoveries, of loans and leases that have been written-off.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amount of expense related to estimated loss from loan and lease transactions.

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