Borrowings (Schedule of Amounts Outstanding and Interest Rates of Short-term Borrowings) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Debt Disclosure [Abstract]
Balance outstanding at end of year	$ 398,932	$ 192,681	$ 247,928
Average daily balance outstanding	271,281	261,335	220,847
Maximum balance outstanding at any month end	$ 398,932	$ 346,786	$ 332,321
Weighted average interest rate for the year	0.19%	0.21%	0.34%
Weighted average interest rate at end of year	0.16%	0.18%	0.19%