Securities (Amortized Cost and Fair Value of Debt Securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Debt Securities Available for Sale, Due in one year or less, Amortized cost	$ 17,746
Debt Securities Available for Sale, Due after one year through five years, Amortized cost	1,018,866
Debt Securities Available for Sale, Due after five years through ten years, Amortized cost	2,995,003
Debt Securities Available for Sale, Due after ten years, Amortized cost	2,053,694
Securities Available for Sale, Gross Amortized cost	6,085,309	$ 6,310,214
Debt Securities Available for Sale, Due in one year or less, Fair value	17,540
Debt Securities Available for Sale, Due after one year through five years, Fair value	957,682
Debt Securities Available for Sale, Due after five years through ten years, Fair value	2,592,296
Debt Securities Available for Sale, Due after ten years, Fair value	1,620,638
Total available for sale debt securities, Fair value	5,188,156	5,556,041
Debt Securities Held to Maturity, Due in one year or less, Amortized cost	103,187
Debt Securities Held to Maturity, Due after one year through five years, Amortized cost	650,946
Debt Securities Held to Maturity, Due after five years through ten years, Amortized cost	795,800
Debt Securities Held to Maturity, Due after ten years, Amortized cost	1,178,012
Total held to maturity debt securities, Amortized cost	2,727,945	2,852,495
Debt Securities Held to Maturity, Due in one year or less, Fair value	100,661
Debt Securities Held to Maturity, Due after one year through five years, Fair value	602,263
Debt Securities Held to Maturity, Due after five years through ten years, Fair value	718,439
Debt Securities Held to Maturity, Due after ten years, Fair value	1,008,924
Total held to maturity debt securities, Fair value	$ 2,430,287	$ 2,615,398