Securities Available for Sale and Held to Maturity - Contractual Maturities of Available for Sale and Held to Maturity Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Securities Available for Sale, Amortized Cost [Abstract]
Due in one year or less	$ 51,084
Due after one year through five years	346,269
Due after five years through ten years	6,188
Due after ten years	4,609
Total amortized cost, before mortgage-backed securities	408,150
Mortgage-backed securities	1,620,713
Securities Available for Sale, Amortized Cost	2,028,863	$ 2,270,709
Securities Available for Sale, Estimated Fair Value [Abstract]
Due in one year or less	49,189
Due after one year through five years	315,552
Due after five years through ten years	5,794
Due after ten years	4,363
Total fair value, before mortgage-backed securities	374,898
Mortgage-backed securities	1,391,276
Total	1,766,174	2,024,082
Securities Held to Maturity, Amortized Cost [Abstract]
Due in one year or less	341
Due after one year through five years	28,872
Due after five years through ten years	0
Due after ten years	0
Total amortized cost, before mortgage-backed securities	29,213
Mortgage-backed securities	1,409,074
Securities Held to Maturity, Amortized Cost	1,438,287	1,494,514
Securities Held to Maturity, Estimated Fair Value [Abstract]
Due in one year or less	341
Due after one year through five years	27,886
Due after five years through ten years	0
Due after ten years	0
Total fair value, before mortgage-backed securities	28,227
Mortgage-backed securities	1,284,644
Total	$ 1,312,871	$ 1,406,589