v3.8.0.1
Securities - Schedule of Securities in a Continuous Unrealized Loss Position Aggregated by Investment Category and Length of Time (Details) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]    
Less than 12 months, Fair Value $ 287,837 $ 464,524
Less than 12 months, Unrealized Loss (2,674) (9,784)
12 months or more, Fair Value 67,391  
12 months or more, Unrealized Loss (3,966)  
Total, Fair Value 355,228 464,524
Total, Unrealized Loss (6,640) (9,784)
U.S. Treasury Securities    
Schedule Of Available For Sale Securities [Line Items]    
Less than 12 months, Fair Value 495 297
Less than 12 months, Unrealized Loss (4) (3)
Total, Fair Value 495 297
Total, Unrealized Loss (4) (3)
Agency Mortgage-backed Securities    
Schedule Of Available For Sale Securities [Line Items]    
Less than 12 months, Fair Value 287,342 445,591
Less than 12 months, Unrealized Loss (2,670) (7,414)
12 months or more, Fair Value 58,044  
12 months or more, Unrealized Loss (1,794)  
Total, Fair Value 345,386 445,591
Total, Unrealized Loss (4,464) (7,414)
Beneficial interests in FHLMC securitization    
Schedule Of Available For Sale Securities [Line Items]    
Less than 12 months, Fair Value   18,636
Less than 12 months, Unrealized Loss   (2,367)
12 months or more, Fair Value 9,347  
12 months or more, Unrealized Loss (2,172)  
Total, Fair Value 9,347 18,636
Total, Unrealized Loss $ (2,172) $ (2,367)