Short and Long-Term Funding (Long-term Funding Narrative) (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended			9 Months Ended
	Aug. 13, 2018	Nov. 30, 2014	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Long-Term Funding
Carrying Value of Securities Purchased under Agreements to Resell and Deposits Paid for Securities Borrowed			$ 246,000			$ 246,000
Fixed Interest Rates, Finance Leases			1.00%
FHLB advances			$ 1,706,763			1,706,763		$ 3,180,967
Increase Decrease in FHLB Advances			$ (1,500,000)			$ (1,500,000)
Decrease in FHLB Advances, Percent			46.00%			46.00%
Prepayment of FHLB advances			$ 950,000
Loss on prepayments of FHLB advances			$ 44,650		$ 0	$ 44,650	$ 0
Net increase (decrease) in short-term FHLB advances						$ (520,000)	$ (685,000)
Minimum
Long-Term Funding
PPPLF Original Terms				2 years
Maximum
Long-Term Funding
PPPLF Original Terms				5 years
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%
PPP
Long-Term Funding
Debt Instrument, Interest Rate, Stated Percentage			0.35%			0.35%
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%