Loans Receivable and Allowance for Credit Losses (Composition of Non-PCI and PCI Loans - Narrative) (Details) $ in Thousands	6 Months Ended
Jun. 30, 2018 USD ($) property_unit	Dec. 31, 2017 USD ($)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment pledged as collateral \| $	$ 19,634,818	$ 18,880,598
Consumer lending \| Single-family residential and home equity line of credit
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loan-to-value ratio (or less at origination)	60.00%
Multifamily \| Commercial lending \| Minimum
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Number of units secured by smaller multifamily properties	5
Multifamily \| Commercial lending \| Maximum
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Number of units secured by smaller multifamily properties	15

Carrying amount as of the balance sheet date of loans that have been pledged as collateral for borrowings. If the secured party has the right by contract or custom to sell or re-pledge the collateral, then the debtor reclassifies that asset and report that asset in its statement of financial position separately from other assets not so encumbered.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5086-111524

Name:	us-gaap_LoansPledgedAsCollateral
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant