Short-Term Borrowings (Details) (Securities Sold under Agreements to Repurchase [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Securities Sold under Agreements to Repurchase [Member]
Securities sold under agreements to repurchase [Line Items]
Ending balance	$ 327,428	$ 310,463	$ 303,786
Weighted average interest rate	0.15%	0.14%	0.12%
Average amount outstanding during year	337,649	312,729	287,176
Weighted average interest rate during year	0.14%	0.14%	0.18%
Maximum balance outstanding at any month-end	$ 357,976	$ 335,193	$ 313,626