Long-term Debt and Short-term Borrowings (Components of Short-term Borrowings) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Debt Disclosure [Abstract]
Total Balance at December 31,	$ 201,243	$ 313,757	$ 499,226
Weighted average interest rate at December 31,	0.16%	0.24%	0.30%
Maximum month end balance during the year	398,853	452,903	543,690
Average amount outstanding during the year	$ 320,338	$ 389,583	$ 480,700
Weighted average interest rate during the year	0.19%	0.27%	0.40%