Short and Long-Term Funding (Long-term Funding Narrative) (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended
	Aug. 13, 2018	Nov. 30, 2014	Mar. 31, 2021	Dec. 31, 2020
Long-Term Funding
Carrying Value of Securities Purchased under Agreements to Resell and Deposits Paid for Securities Borrowed			$ 192,000
Fixed Interest Rates, Finance Leases			1.00%
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances			$ 1,629,966	$ 1,632,723
Two Thousand Eighteen Senior Notes [Member] [Domain]
Long-Term Funding
Debt Instrument, Issuance Date Month, Year	August 2018
New Senior Debt Issued	$ 300,000
Debt Instrument, Maturity Date Month, Year	August 2021
Debt Instrument Call Date Earliest Month Year	July 2021
Debt Instrument, Interest Rate, Stated Percentage	3.50%
Two Thousand Fourteen Subordinated Notes
Long-Term Funding
Debt Instrument, Issuance Date Month, Year		November 2014
Junior Subordinated Debentures Issued		$ 250,000
Debt Instrument, Term		10 years
Debt Instrument, Maturity Date Month, Year		January 2025
Debt Instrument Call Date Earliest Month Year		October 2024
Subordinated Borrowing, Interest Rate		4.25%