Investments In Securities - Unrealized Gain or Loss Position and Components of Carrying Value of Available for Sale Securities (Details) - USD ($)
$ in Thousands |
Sep. 30, 2020 |
Dec. 31, 2019 |
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Principal Amount |
$ 1,893,769
|
$ 11,324,705
|
| Amortized Cost |
1,952,400
|
11,586,293
|
| Gross Unrealized Loss |
(34)
|
(792)
|
| Gross Unrealized Gain |
200,231
|
356,265
|
| Fair Value |
2,152,597
|
11,941,766
|
| Fannie Mae |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Principal Amount |
1,468,314
|
8,779,331
|
| Amortized Cost |
1,510,059
|
8,975,140
|
| Gross Unrealized Loss |
(22)
|
(291)
|
| Gross Unrealized Gain |
181,302
|
294,937
|
| Fair Value |
1,691,339
|
9,269,786
|
| Freddie Mac |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Principal Amount |
407,397
|
2,522,870
|
| Amortized Cost |
423,830
|
2,587,512
|
| Gross Unrealized Loss |
0
|
(40)
|
| Gross Unrealized Gain |
18,746
|
61,323
|
| Fair Value |
442,576
|
2,648,795
|
| Ginnie Mae |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Principal Amount |
18,058
|
22,504
|
| Amortized Cost |
18,511
|
23,641
|
| Gross Unrealized Loss |
(12)
|
(461)
|
| Gross Unrealized Gain |
183
|
5
|
| Fair Value |
$ 18,682
|
$ 23,185
|