Schedule II - Valuation and Qualifying Accounts (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Valuation and Qualifying Accounts [Roll Forward]
Balance Beginning of Year	$ 1,678	$ 1,467	$ 1,364
Charged to Costs and Expenses	7,409	6,652	5,138
Write-offs, Net of Recoveries and Actual Returns	(6,331)	(6,441)	(5,035)
Balance at End of Year	2,756	1,678	1,467
Allowance for doubtful accounts
Valuation and Qualifying Accounts [Roll Forward]
Balance Beginning of Year	936	898	727
Charged to Costs and Expenses	1,422	446	616
Write-offs, Net of Recoveries and Actual Returns	(537)	(408)	(445)
Balance at End of Year	1,821	936	898
Allowance for returns
Valuation and Qualifying Accounts [Roll Forward]
Balance Beginning of Year	742	569	637
Charged to Costs and Expenses	5,987	6,206	4,522
Write-offs, Net of Recoveries and Actual Returns	(5,794)	(6,033)	(4,590)
Balance at End of Year	$ 935	$ 742	$ 569