Valuation and Qualifying accounts (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Allowance for Doubtful Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation Allowances and Reserves, Opening Balance	$ 390	$ 361	$ 350
Valuation Allowances and Reserves, Charged to Cost and Expense	48	30	22
Valuation Allowances and Reserves, Adjustments	8	1	11
Valuation Allowances and Reserves, Closing Balance	430	390	361
Allowance for Sales Returns [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation Allowances and Reserves, Opening Balance	1,411	584	827
Valuation Allowances and Reserves, Charged to Cost and Expense	4,265	6,750	5,396
Valuation Allowances and Reserves, Adjustments	5,247	5,923	5,639
Valuation Allowances and Reserves, Closing Balance	$ 429	$ 1,411	$ 584