Securities - Scheduled Contractual Maturities of HTM Debt Securities (Details) $ in Thousands	Sep. 30, 2025 USD ($)
Amortized cost
Within One Year	$ 0
After One Year through Five Years	686,181
After Five Years through Ten Years	635,844
After Ten Years	1,558,657
Total	2,880,682
Fair value
Within One Year	0
After One Year through Five Years	654,592
After Five Years through Ten Years	549,160
After Ten Years	1,263,610
Total	$ 2,467,362
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	1.13%
After Five Years through Ten Years	1.89%
After Ten Years	1.80%
Total	1.66%
U.S. Treasury securities
Amortized cost
Within One Year	$ 0
After One Year through Five Years	539,255
After Five Years through Ten Years	0
After Ten Years	0
Total	539,255
Fair value
Within One Year	0
After One Year through Five Years	519,800
After Five Years through Ten Years	0
After Ten Years	0
Total	$ 519,800
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	105,322
After Five Years through Ten Years	467,017
After Ten Years	434,263
Total	1,006,602
Fair value
Within One Year	0
After One Year through Five Years	96,630
After Five Years through Ten Years	403,405
After Ten Years	354,062
Total	$ 854,097
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	1.37%
After Five Years through Ten Years	1.93%
After Ten Years	1.98%
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	41,604
After Five Years through Ten Years	168,827
After Ten Years	938,382
Total	1,148,813
Fair value
Within One Year	0
After One Year through Five Years	38,162
After Five Years through Ten Years	145,755
After Ten Years	764,180
Total	$ 948,097
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	1.54%
After Five Years through Ten Years	1.77%
After Ten Years	1.68%
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	186,012
Total	186,012
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	0
After Ten Years	145,368
Total	$ 145,368
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	2.02%
Total	2.02%