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INVESTMENT SECURITIES - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Schedule Of Investments [Line Items]      
Percentage Of Debt Securities Government And Government Sponsored Agencies 99.00%    
Amortized cost $ 1,917,382   $ 1,975,230
Fair value 1,905,230   $ 1,942,568
Available for sale Securities [Member] | Private label MBS [Member]      
Schedule Of Investments [Line Items]      
Other Than Temporary Impairment Credit Losses Recognized In Earnings Additions Additional Credit Losses $ 0 $ 0  
Loans Receivable, Description of Variable Rate Basis The interest rate on these private-label MBS is variable, tied to 3-month LIBOR and limited to the weighted-average coupon on the underlying collateral.    
Available for sale Securities [Member] | Private label MBS [Member] | FICO Score, Greater than 700 [Member] | LTV Less than 80 Percent [Member]      
Schedule Of Investments [Line Items]      
Financing Receivable, Credit Quality, Additional Information The underlying mortgages are fixed-rate, single-family loans with original FICO scores (over 700) and moderate loan-to-value ratios (under 80%), as well as moderate delinquency levels.    
Available for sale Securities [Member] | PRHFA [Member] | Zero-coupon bonds [Member]      
Schedule Of Investments [Line Items]      
Amortized cost $ 8,200    
Fair value 7,000    
Available for sale Securities [Member] | PRHFA [Member] | Zero-coupon bonds [Member] | Residential pass-through mortgage-backed securities [Member]      
Schedule Of Investments [Line Items]      
Amortized cost 4,200    
Fair value $ 2,900    
Held-to-maturity Securities [Member]      
Schedule Of Investments [Line Items]      
Percentage Of Held To Maturity Securities 70.00%