Securities - Scheduled Contractual Maturities of HTM Debt Securities (Details) $ in Thousands	Sep. 30, 2022 USD ($)
Amortized cost
Within One Year	$ 0
After One Year through Five Years	285,325
After Five Years through Ten Years	589,529
After Ten Years	2,137,813
Total	3,012,667
Fair value
Within One Year	0
After One Year through Five Years	255,365
After Five Years through Ten Years	507,930
After Ten Years	1,695,840
Total	$ 2,459,135
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	0.96%
After Five Years through Ten Years	1.55%
After Ten Years	1.75%
Total	1.64%
U.S. Treasury securities
Amortized cost
Within One Year	$ 0
After One Year through Five Years	285,325
After Five Years through Ten Years	237,388
After Ten Years	0
Total	522,713
Fair value
Within One Year	0
After One Year through Five Years	255,365
After Five Years through Ten Years	210,720
After Ten Years	0
Total	$ 466,085
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	0.96%
After Five Years through Ten Years	1.14%
After Ten Years	0.00%
Total	1.05%
U.S. government-sponsored enterprises debt securities
Amortized cost
Within One Year	$ 0
After One Year through Five Years	0
After Five Years through Ten Years	255,708
After Ten Years	742,525
Total	998,233
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	215,684
After Ten Years	566,933
Total	$ 782,617
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	0.00%
After Five Years through Ten Years	1.94%
After Ten Years	1.88%
Total	1.90%
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities
Amortized cost
Within One Year	$ 0
After One Year through Five Years	0
After Five Years through Ten Years	96,433
After Ten Years	1,205,391
Total	1,301,824
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	81,526
After Ten Years	984,813
Total	$ 1,066,339
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	0.00%
After Five Years through Ten Years	1.56%
After Ten Years	1.63%
Total	1.63%
Municipal securities
Amortized cost
Within One Year	$ 0
After One Year through Five Years	0
After Five Years through Ten Years	0
After Ten Years	189,897
Total	189,897
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	0
After Ten Years	144,094
Total	$ 144,094
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	0.00%
After Five Years through Ten Years	0.00%
After Ten Years	1.97%
Total	1.97%