Securities (Schedule of Contractual Maturities of Investment Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, Year One	$ 61,198
Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year One Through Five	781,405
Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10	1,526,384
Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 10	2,404,755
Debt securities available-for-sale, amortized cost	4,773,742	$ 4,997,529
Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One	61,791
Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five	807,659
Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10	1,559,371
Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10	2,403,098
Debt securities available for sale at fair value	4,831,919	5,210,134
Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, Year One	0
Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, after Year One through Five	72,430
Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, after Year Five through Ten	1,235,888
Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, after Year 10	766,840
Debt Securities, Held-to-Maturity, Amortized Cost	2,075,158	0
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Fair Value	0
Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five	72,215
Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10	1,233,393
Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10	765,443
Debt Securities, Held-to-maturity, Fair Value	$ 2,071,051	$ 0