Securities Available for Sale and Held to Maturity - Contractual Maturities of Available for Sale and Held to Maturity Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Securities Available for Sale, Amortized Cost [Abstract]
Due in one year or less	$ 1,243
Due after one year through five years	277,977
Due after five years through ten years	112,990
Due after ten years	10,153
Total amortized cost, before mortgage-backed securities	402,363
Mortgage-backed securities	2,788,966
Securities Available for Sale, Amortized Cost	3,191,329	$ 3,256,289	$ 3,256,289
Securities Available for Sale, Estimated Fair Value [Abstract]
Due in one year or less	1,242
Due after one year through five years	263,670
Due after five years through ten years	105,167
Due after ten years	9,725
Total fair value, before mortgage-backed securities	379,804
Mortgage-backed securities	2,638,442
Total	3,018,246	3,238,877
Securities Held to Maturity, Amortized Cost [Abstract]
Due in one year or less	2,807
Due after one year through five years	4,517
Due after five years through ten years	0
Due after ten years	0
Total amortized cost, before mortgage-backed securities	7,324
Mortgage-backed securities	600,274
Securities Held to Maturity, Amortized Cost	607,598	342,537
Securities Held to Maturity, Estimated Fair Value [Abstract]
Due in one year or less	2,815
Due after one year through five years	4,534
Due after five years through ten years	0
Due after ten years	0
Total fair value, before mortgage-backed securities	7,349
Mortgage-backed securities	586,855
Total	$ 594,204	$ 353,511