Mortgage-Backed Securities - Gross Unrealized Losses (Details) $ in Thousands	Sep. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Agency MBS
Investments [Line Items]
Fair value, Less than 12 Months	$ 5,316	$ 346,064
Gross Unrealized Losses, Less than 12 Month	$ 69	$ 22,808
Number of Securities, Less than 12 Months	4	79
Fair value, 12 Months or Longer	$ 903,296	$ 697,514
Gross Unrealized Losses, 12 Months or Longer	$ 217,559	$ 156,411
Number of Securities, 12 Months or Longer	84	17
Non-Agency MBS
Investments [Line Items]
Fair value, Less than 12 Months	$ 2,487	$ 42,162
Gross Unrealized Losses, Less than 12 Month	$ 59	$ 1,787
Number of Securities, Less than 12 Months	8	56
Fair value, 12 Months or Longer	$ 26,615	$ 12,195
Gross Unrealized Losses, 12 Months or Longer	$ 1,358	$ 847
Number of Securities, 12 Months or Longer	45	22