Short-Term Borrowings and Long-Term Debt Short Term (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Short-term Debt [Line Items]
Maximum borrowing capacity	$ 1,000,000
Short-term borrowings	497,663	$ 329,719	$ 1,258,629
Collateralized borrowings availability at discount window	1,200,000	1,100,000
Federal funds purchased
Short-term Debt [Line Items]
Short-term borrowings	197,235	6,219	582,436
Maximum month-end outstanding amount	266,338	577,581	848,179
Short-term FHLB advances
Short-term Debt [Line Items]
Short-term borrowings	110,000	70,000	400,000
Maximum month-end outstanding amount	200,000	600,000	600,000
Customer repurchase agreements
Short-term Debt [Line Items]
Short-term borrowings	111,496	158,394	175,621
Maximum month-end outstanding amount	212,509	244,729	215,305
Customer short-term promissory notes
Short-term Debt [Line Items]
Short-term borrowings	78,932	95,106	100,572
Maximum month-end outstanding amount	$ 93,176	$ 95,106	$ 115,129