Short-Term Borrowings (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Securities Sold under Agreements to Repurchase [Member]
Short-term borrowings [Line Items]
Ending balance	$ 297,199	$ 304,467	$ 327,428
Weighted average interest rate	0.06%	0.11%	0.15%
Average amount outstanding during year	$ 327,559	$ 326,056	$ 337,649
Weighted average interest rate during year	0.07%	0.12%	0.14%
Maximum balance outstanding at any month-end	$ 372,236	$ 361,231	$ 357,976
Federal Home Loan Bank Advances [Member]
Short-term borrowings [Line Items]
Ending balance	$ 100,000	$ 60,000
Weighted average interest rate	0.34%	0.25%
Average amount outstanding during year	$ 89,208	$ 6,726
Weighted average interest rate during year	0.23%	0.27%
Maximum balance outstanding at any month-end	$ 280,000	$ 60,000
Federal Funds Purchased [Member]
Short-term borrowings [Line Items]
Ending balance	$ 0	$ 25,000
Weighted average interest rate	0.00%	0.40%
Average amount outstanding during year	$ 3,762	$ 2,003
Weighted average interest rate during year	0.37%	0.40%
Maximum balance outstanding at any month-end	$ 22,000	$ 25,000