Short-Term Borrowings (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Securities Sold under Agreements to Repurchase [Member]
Short-term borrowings [Line Items]
Ending balance	$ 304,467	$ 327,428	$ 310,463
Weighted average interest rate	0.11%	0.15%	0.14%
Average amount outstanding during year	326,056	337,649	312,729
Weighted average interest rate during year	0.12%	0.14%	0.14%
Maximum balance outstanding at any month-end	361,231	357,976	335,193
Federal Home Loan Bank Advances [Member]
Short-term borrowings [Line Items]
Ending balance	60,000
Weighted average interest rate	0.25%
Average amount outstanding during year	6,726
Weighted average interest rate during year	0.27%
Maximum balance outstanding at any month-end	60,000
Federal Funds Purchased [Member]
Short-term borrowings [Line Items]
Ending balance	25,000
Weighted average interest rate	0.40%
Average amount outstanding during year	2,003
Weighted average interest rate during year	0.40%
Maximum balance outstanding at any month-end	$ 25,000