Quarterly Financial Data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenue, Net	$ 79,896	$ 77,457	$ 78,677	$ 73,230	$ 77,941	$ 82,815	$ 78,661	$ 74,299
Gross Profit	39,685	38,147	37,542	36,027	38,945	40,955	38,038	36,794	151,401	154,732	156,510
Net Income	$ 7,372	$ 6,428	$ 5,878	$ 6,657	$ 13,332	$ 11,034	$ 7,367	$ 8,685	$ 26,335	$ 40,418	$ 41,281
Basic	$ 0.48	$ 0.42	$ 0.39	$ 0.44	$ 0.89	$ 0.75	$ 0.50	$ 0.60	$ 1.72	$ 2.75	$ 2.90
Diluted	$ 0.46	$ 0.42	$ 0.38	$ 0.43	$ 0.86	$ 0.72	$ 0.48	$ 0.58	$ 1.68	$ 2.65	$ 2.80