Summary of Significant Accounting Policies (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Expense for uncollectible accounts and accounts written off
Expense for Uncollectible Accounts	$ 1,345	$ 1,818	$ 1,155
Accounts Written Off	$ 1,484	$ 2,456	$ 2,096