To Be Announced RMBS (Details) - USD ($) $ in Thousands |
Sep. 30, 2017 |
Dec. 31, 2016 |
||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| To Be Announced Securities [Line Items] | ||||||||||||||||||||
| Fair Value | $ 1,756,432 | $ 1,505,026 | ||||||||||||||||||
| Financial Instruments Sold, Not yet Purchased, at Fair Value | (675,650) | (584,896) | ||||||||||||||||||
| Payable for securities purchased | (169,717) | (85,168) | ||||||||||||||||||
| To Be Announced Fixed Rate Agency Securities [Member] | ||||||||||||||||||||
| To Be Announced Securities [Line Items] | ||||||||||||||||||||
| Fair Value | 121,009 | [1],[2],[3] | 70,525 | [4],[5],[6] | ||||||||||||||||
| Investment Owned, Balance, Principal Amount | 115,303 | 67,720 | ||||||||||||||||||
| Receivable for securities sold | 471,626 | 406,708 | ||||||||||||||||||
| TBA - Fixed Rate Agency Securities Sold Short [Member] | ||||||||||||||||||||
| To Be Announced Securities [Line Items] | ||||||||||||||||||||
| Financial Instruments Sold, Not yet Purchased, at Fair Value | (470,487) | [2],[7] | (404,728) | [5],[8] | ||||||||||||||||
| Investment Sold, Not yet Purchased, Balance, Principal Amount | (447,590) | (384,155) | ||||||||||||||||||
| Payable for securities purchased | (121,353) | (70,347) | ||||||||||||||||||
| Investment Owned At Fair Value, Net | $ (349,478) | $ (334,203) | ||||||||||||||||||
| ||||||||||||||||||||