Short-Term Borrowings (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Short-term Debt [Line Items]
Balance at year-end	$ 681,703	$ 442,481
FHLB, unused lines of credit available for short-term financing	1,900,000	2,100,000
Federal Funds Purchased [Member]
Short-term Debt [Line Items]
Balance at year-end	50,000	99,500	$ 68,000
Average during the year	65,257	97,424	110,154
Maximum month end balance	$ 85,000	$ 159,000	$ 183,000
Weighted average rate during the year	0.98%	0.36%	0.29%
Weighted average rate at December 31	1.19%	0.51%	0.34%
Securities Sold under Repurchase Agreements [Member]
Short-term Debt [Line Items]
Balance at year-end	$ 173,703	$ 167,981	$ 148,802
Average during the year	168,821	162,201	165,858
Maximum month end balance	$ 189,875	$ 178,326	$ 182,861
Weighted average rate during the year	0.06%	0.06%	0.06%
Weighted average rate at December 31	0.07%	0.06%	0.06%
Other Short-Term Borrowings [Member]
Short-term Debt [Line Items]
Balance at year-end	$ 458,000	$ 175,000	$ 100,000
Average during the year	263,575	80,260	106,438
Maximum month end balance	$ 424,000	$ 175,000	$ 320,000
Weighted average rate during the year	0.59%	0.42%	0.40%
Weighted average rate at December 31	0.70%	0.56%	0.36%