Short and Long-Term Funding (Components of Short-term and Long-term Funding) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Short-term Funding [Abstract]
Federal funds purchased	$ 25,890	$ 141,950
Securities sold under agreements to repurchase	140,666	182,865
Federal funds purchased and securities sold under agreements to repurchase	166,556	324,815
Commercial paper	43,604	67,467
Total short-term funding	210,159	392,282
Long-term Funding
Senior notes, at par	550,000	250,000
Subordinated notes, at par	250,000	250,000
Other long-term funding and capitalized costs	(4,785)	(2,718)
Total long-term funding	795,215	497,282
TotalShortTermLongTermExcludingFHLB	1,005,375	889,564
Advances from Federal Home Loan Banks [Abstract]
ShortTermFHLBAdvances	405,000	284,000
LongTermFHLBAdvances	2,927,655	2,900,168
TotalFHLB_Advances	3,332,655	3,184,168
Total short and long-term funding, excluding FHLB advances	$ 4,338,030	$ 4,073,732