Quarterly report pursuant to Section 13 or 15(d)

Available-for-Sale Securities, at Fair Value Schedule of Unrealized Loss on Investments (Details)

v3.8.0.1
Available-for-Sale Securities, at Fair Value Schedule of Unrealized Loss on Investments (Details)
$ in Thousands
Sep. 30, 2017
USD ($)
position
Dec. 31, 2016
USD ($)
position
Schedule of Available-for-sale Securities [Line Items]    
Available-for-Sale Securities, Number of Positions | position 1,380 1,239
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | position 152 252
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | position 164 125
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Percent Agency 95.10% 95.80%
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value $ 4,136,362 $ 6,416,820
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses (22,669) (204,034)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 2,341,707 504,978
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses (98,029) (39,955)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value 6,478,069 6,921,798
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses (120,698) (243,989)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value $ 3,934,443 $ 6,147,713