Securities (Scheduled Contractual Maturities of HTM Debt Securities) (Details) $ in Thousands	Mar. 31, 2022 USD ($)
Amortized cost
Within One Year	$ 0
After One Year through Five Years	24,415
After Five Years through Ten Years	746,591
After Ten Years	2,226,696
Total	2,997,702
Fair value
Within One Year	0
After One Year through Five Years	23,492
After Five Years through Ten Years	712,673
After Ten Years	2,079,803
Total	$ 2,815,968
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	0.76%
After Five Years through Ten Years	1.21%
After Ten Years	1.73%
Total	1.59%
U.S. Treasury securities
Amortized cost
Within One Year	$ 0
After One Year through Five Years	24,415
After Five Years through Ten Years	495,574
After Ten Years	0
Total	519,989
Fair value
Within One Year	0
After One Year through Five Years	23,492
After Five Years through Ten Years	475,783
After Ten Years	0
Total	$ 499,275
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	0.76%
After Five Years through Ten Years	1.06%
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	162,903
After Ten Years	783,860
Total	946,763
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	153,074
After Ten Years	726,212
Total	$ 879,286
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	0.00%
After Five Years through Ten Years	1.43%
After Ten Years	1.86%
Total	1.79%
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	88,114
After Ten Years	1,252,565
Total	1,340,679
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	83,816
After Ten Years	1,180,495
Total	$ 1,264,311
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	0.00%
After Five Years through Ten Years	1.61%
After Ten Years	1.62%
Total	1.62%
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	190,271
Total	190,271
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	0
After Ten Years	173,096
Total	$ 173,096
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%