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
Mar. 31, 2018
USD ($)
position
Dec. 31, 2017
USD ($)
position
Schedule of Available-for-sale Securities [Line Items]    
Available-for-Sale Securities, Number of Positions | position 1,443 1,435
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | position 503 253
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | position 227 234
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Percent Agency 98.50% 98.50%
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value $ 15,120,927 $ 12,198,870
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses (347,280) (65,313)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 2,355,005 2,464,544
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses (172,142) (114,724)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value 17,475,932 14,663,414
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses (519,422) (180,037)
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 $ 14,891,094 $ 12,010,451