Nature of Operations and Summary of Significant Accounting Policies Revenue Recognition and Other Costs (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Deferred Revenue Arrangement [Line Items]
Earned revenue	$ 219,315	$ 240,239	$ 295,530
Amounts billed to customers	265,686	239,600	298,131
Shipping revenue	(8,595)	(6,537)	(5,507)
Research and development costs	4,375	3,858	3,256
Cost of Sales [Member]
Deferred Revenue Arrangement [Line Items]
Shipping costs	11,443	8,488	5,942
Selling, General and Administrative Expense [Member]
Deferred Revenue Arrangement [Line Items]
Advertising costs	$ 4,548	$ 3,268	$ 3,355