Debt Securities - Maturity Schedule (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Available-for-Sale, Amortized Cost
Due within one year	$ 1,315
Due after one year through five years	856,275
Due after five years through ten years	38,723
Due after ten years	40,438
Total before mortgage-backed securities	936,751
Mortgage-backed securities	4,473,736
Amortized Cost	5,410,487	$ 5,930,103
Available-for-Sale, Fair Value
Due within one year	1,302
Due after one year through five years	782,020
Due after five years through ten years	36,427
Due after ten years	36,844
Total before mortgage-backed securities	856,593
Mortgage-backed securities	3,885,145
Debt securities, available-for-sale	4,741,738	5,307,307
Held-to-Maturity, Amortized Cost
Due within one year	4,558
Due after one year through five years	924,257
Due after five years through ten years	172,780
Due after ten years	1,407,784
Total before mortgage-backed securities	2,509,379
Mortgage-backed securities	1,044,426
Amortized Cost	3,553,805	3,715,052
Held-to-Maturity, Fair Value
Due within one year	4,533
Due after one year through five years	827,398
Due after five years through ten years	159,696
Due after ten years	1,112,479
Total before mortgage-backed securities	2,104,106
Mortgage-backed securities	934,361
Total	$ 3,038,467	$ 3,274,792