Short and Long-Term Funding (Long-term Funding Narrative) (Details) - USD ($) $ in Thousands			1 Months Ended	3 Months Ended
	Jul. 13, 2021	Aug. 13, 2018	Nov. 30, 2014	Jun. 30, 2021	Dec. 31, 2020
Long-Term Funding
Carrying Value of Securities Purchased under Agreements to Resell and Deposits Paid for Securities Borrowed				$ 260,000
Fixed Interest Rates, Finance Leases				1.07%
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances				$ 1,619,826	$ 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, Redemption	Jul. 13, 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%