Borrowings (Schedule of Amounts Outstanding and Interest Rates of Short-term Borrowings) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Borrowings [Abstract]
Balance outstanding at end of year	$ 192,535	$ 202,928	$ 193,930
Average daily balance outstanding	188,630	202,423	188,663
Maximum balance outstanding at any month end	$ 232,008	$ 287,334	$ 268,197
Weighted average interest rate for the year	0.30%	0.35%	0.63%
Weighted average interest rate at end of year	0.18%	0.22%	0.45%