Short and Long-Term Funding (Components of Short-term and Long-term Funding) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Short-term Funding [Abstract]
Federal funds purchased	$ 20,720	$ 141,950
Securities sold under agreements to repurchase	183,013	182,865
Federal funds purchased and securities sold under agreements to repurchase	203,733	324,815
Commercial paper	52,791	67,467
Total short-term funding	256,525	392,282
Long-term Funding
Senior notes, at par	250,000	250,000
Subordinated notes, at par	250,000	250,000
Other long-term funding and capitalized costs	(2,381)	(2,718)
Total long-term funding	497,619	497,282
TotalShortTermLongTermExcludingFHLB	754,144	889,564
Advances from Federal Home Loan Banks [Abstract]
ShortTermFHLBAdvances	370,000	284,000
LongTermFHLBAdvances	4,427,857	2,900,168
TotalFHLB_Advances	4,797,857	3,184,168
Total short and long-term funding, excluding FHLB advances	$ 5,552,001	$ 4,073,732