Schedule II - Valuation and Qualifying Accounts (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Valuation and Qualifying Accounts [Roll Forward]
Balance Beginning of Year	$ 1,364	$ 1,894	$ 1,696
Charged to Costs and Expenses	5,138	5,008	5,180
Write-offs, Net of Recoveries and Actual Returns	(5,035)	(5,538)	(4,982)
Balance at End of Year	1,467	1,364	1,894
Allowance for doubtful accounts
Valuation and Qualifying Accounts [Roll Forward]
Balance Beginning of Year	727	972	1,139
Charged to Costs and Expenses	616	467	306
Write-offs, Net of Recoveries and Actual Returns	(445)	(712)	(473)
Balance at End of Year	898	727	972
Allowance for returns
Valuation and Qualifying Accounts [Roll Forward]
Balance Beginning of Year	637	922	557
Charged to Costs and Expenses	4,522	4,541	4,874
Write-offs, Net of Recoveries and Actual Returns	(4,590)	(4,826)	(4,509)
Balance at End of Year	$ 569	$ 637	$ 922