Securities - Scheduled Contractual Maturities of HTM Debt Securities (Details) $ in Thousands	Sep. 30, 2024 USD ($)
Amortized cost
Within One Year	$ 0
After One Year through Five Years	538,386
After Five Years through Ten Years	462,682
After Ten Years	1,927,331
Total	2,928,399
Fair value
Within One Year	0
After One Year through Five Years	509,546
After Five Years through Ten Years	409,605
After Ten Years	1,591,201
Total	$ 2,510,352
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	1.05%
After Five Years through Ten Years	1.83%
After Ten Years	1.79%
Total	1.66%
U.S. Treasury securities
Amortized cost
Within One Year	$ 0
After One Year through Five Years	533,683
After Five Years through Ten Years	0
After Ten Years	0
Total	533,683
Fair value
Within One Year	0
After One Year through Five Years	505,144
After Five Years through Ten Years	0
After Ten Years	0
Total	$ 505,144
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	1.05%
After Five Years through Ten Years	0.00%
After Ten Years	0.00%
Total	1.05%
U.S. government agency and U.S. government-sponsored enterprise debt securities
Amortized cost
Within One Year	$ 0
After One Year through Five Years	0
After Five Years through Ten Years	368,217
After Ten Years	635,730
Total	1,003,947
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	326,454
After Ten Years	522,346
Total	$ 848,800
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	0.00%
After Five Years through Ten Years	1.89%
After Ten Years	1.90%
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	4,703
After Five Years through Ten Years	94,465
After Ten Years	1,103,599
Total	1,202,767
Fair value
Within One Year	0
After One Year through Five Years	4,402
After Five Years through Ten Years	83,151
After Ten Years	920,620
Total	$ 1,008,173
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	1.43%
After Five Years through Ten Years	1.61%
After Ten Years	1.70%
Total	1.69%
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	188,002
Total	188,002
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	0
After Ten Years	148,235
Total	$ 148,235
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	2.00%
Total	2.00%