Loans Receivable and Allowance for Credit Losses (Composition of Non-PCI and PCI Loans - Narrative) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($) property_unit	Dec. 31, 2017 USD ($)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans held-for-investment pledged as collateral | $	$ 20,387,387	$ 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 residential | Commercial lending | Minimum
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Number of units in multifamily properties used to secure multifamily residential loans	5
Multifamily residential | Commercial lending | Maximum
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Number of units in multifamily properties used to secure multifamily residential loans	15