Short-Term Borrowings and Long-Term Debt Short Term (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Short-term Debt [Line Items]
Maximum borrowing capacity	$ 1,100,000
Short-term borrowings	541,317	$ 497,663	$ 329,719
Collateralized borrowings availability at discount window	1,200,000	1,200,000
Federal funds purchased
Short-term Debt [Line Items]
Short-term borrowings	278,570	197,235	6,219
Maximum month-end outstanding amount	449,184	266,338	577,581
Short-term FHLB advances
Short-term Debt [Line Items]
Short-term borrowings	0	110,000	70,000
Maximum month-end outstanding amount	0	200,000	600,000
Customer repurchase agreements
Short-term Debt [Line Items]
Short-term borrowings	195,734	111,496	158,394
Maximum month-end outstanding amount	221,989	212,509	244,729
Customer short-term promissory notes
Short-term Debt [Line Items]
Short-term borrowings	67,013	78,932	95,106
Maximum month-end outstanding amount	$ 77,887	$ 93,176	$ 95,106