| Marketable Securities [Table Text Block] |
| (in thousands) | | | | | | | | | | | | | | | | | | | | | | | | |
| | | September 30, 2026 | | | December 31, 2025 | |
| | | Par Value | | | Cost(1) | | | Fair Value | | | Par Value | | | Cost(1) | | | Fair Value | |
| Fixed-rate RMBS | | $ | 11,091,428 | | | $ | 11,287,456 | | | $ | 10,655,685 | | | $ | 10,345,029 | | | $ | 10,558,236 | | | $ | 10,615,570 | |
| Other(2)(3)(4) | | | - | | | | 14,413 | | | | 11,383 | | | | | | | | 16,103 | | | | 13,088 | |
| Total | | $ | 11,091,428 | | | $ | 11,301,869 | | | $ | 10,667,068 | | | $ | 10,345,029 | | | $ | 10,574,339 | | | $ | 10,628,658 | |
|
| Gain (Loss) on Securities [Table Text Block] |
| (in thousands) | | | | | | | | |
| | | Nine Months Ended September 30, | |
| | | 2026 | | | 2025 | |
| Proceeds from sales of RMBS | | $ | 769,781 | | | $ | 733,904 | |
| Carrying value of RMBS sold | | | (768,857 | ) | | | (743,192 | ) |
| Net gain (loss) on sales of RMBS | | $ | 924 | | | $ | (9,288 | ) |
| | | | | | | | | |
| Gross gain on sales of RMBS | | $ | 924 | | | $ | - | |
| Gross loss on sales of RMBS | | | - | | | | (9,288 | ) |
| Net gain (loss) on sales of RMBS | | $ | 924 | | | $ | (9,288 | ) |
|