Quarterly Financial Information (Summary Of Selected Financial Information) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Quarterly Financial Information [Abstract]
Revenues	$ 82,079	$ 77,184	$ 76,735	$ 73,393	$ 72,439	$ 73,769	$ 72,600	$ 69,820	$ 309,391	$ 288,628	$ 290,286
Gross profit	39,020	36,132	34,137	32,623	32,616	33,207	32,475	30,019	141,912	128,317	128,763
Income before income taxes	13,504	11,818	9,309	9,482	10,159	11,263	10,383	8,094	44,113	39,899	44,638
Net income	$ 8,699	$ 7,506	$ 5,624	$ 5,728	$ 7,210	$ 6,723	$ 6,249	$ 4,872	$ 27,557	$ 25,054	$ 27,010
Earnings per diluted share	$ 0.27	$ 0.23	$ 0.17	$ 0.17	$ 0.21	$ 0.19	$ 0.17	$ 0.13	$ 0.83	$ 0.71	$ 0.74
Shares used in computing diluted earnings per share	32,031	32,960	33,848	33,720	33,895	35,410	36,203	36,655	33,154	35,528	36,624