Securities - Scheduled Contractual Maturities of HTM Debt Securities (Details) $ in Thousands	Mar. 31, 2024 USD ($)
Amortized cost
Within One Year	$ 0
After One Year through Five Years	535,773
After Five Years through Ten Years	438,202
After Ten Years	1,974,667
Total	2,948,642
Fair value
Within One Year	0
After One Year through Five Years	489,801
After Five Years through Ten Years	371,157
After Ten Years	1,553,520
Total	$ 2,414,478
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	530,921
After Five Years through Ten Years	0
After Ten Years	0
Total	530,921
Fair value
Within One Year	0
After One Year through Five Years	485,400
After Five Years through Ten Years	0
After Ten Years	0
Total	$ 485,400
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-sponsored enterprises debt securities
Amortized cost
Within One Year	$ 0
After One Year through Five Years	0
After Five Years through Ten Years	343,666
After Ten Years	659,031
Total	1,002,697
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	291,586
After Ten Years	514,213
Total	$ 805,799
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	0.00%
After Five Years through Ten Years	1.90%
After Ten Years	1.89%
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	4,852
After Five Years through Ten Years	94,536
After Ten Years	1,127,031
Total	1,226,419
Fair value
Within One Year	0
After One Year through Five Years	4,401
After Five Years through Ten Years	79,571
After Ten Years	895,298
Total	$ 979,270
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	1.40%
After Five Years through Ten Years	1.59%
After Ten Years	1.69%
Total	1.68%
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	188,605
Total	188,605
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	0
After Ten Years	144,009
Total	$ 144,009
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	1.99%
Total	1.99%