Significant Accounting Policies Changes in the allowance for doubtful accounts receivable (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at beginning of year	$ 3,698	$ 5,339	$ 6,887
Additions charged to earnings	637	428	2,274
Uncollectible receivables written off, net of recoveries	(1,772)	(2,069)	(3,822)
Balance at end of year	$ 2,563	$ 3,698	$ 5,339