Quarterly Financial Data (Unaudited) - (Details) (USD $)	3 Months Ended										12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012	Jun. 30, 2012		Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenue	$ 107,925,000	[1]	$ 106,418,000	$ 106,705,000	[1]	$ 103,367,000	$ 100,920,000	$ 101,119,000	$ 98,327,000	$ 95,909,000	$ 424,415,000	$ 396,275,000
Direct costs	84,478,000	[1]	83,283,000	83,810,000	[1]	81,515,000	78,126,000	80,152,000	77,594,000	76,112,000	333,086,000	311,984,000	260,172,000
Gross profit	23,447,000	[1]	23,135,000	22,895,000	[1]	21,852,000	22,794,000	20,967,000	20,733,000	19,797,000	91,329,000	84,291,000
Selling, general, and administrative expenses	17,050,000	[1]	16,812,000	16,752,000	[1]	16,253,000	17,336,000	16,391,000	16,056,000	15,198,000	66,867,000	64,981,000	57,305,000
Operating income	6,397,000	[1]	6,323,000	6,143,000	[1]	5,599,000	5,458,000	4,576,000	4,677,000	4,599,000	24,462,000	19,310,000	13,930,000
Interest and other income (expense), net	717,000	[1]	(68,000)	384,000	[1]	(50,000)	(152,000)	50,000	(48,000)	(37,000)	983,000	(187,000)
Income before income taxes	7,114,000	[1]	6,255,000	6,527,000	[1]	5,549,000	5,306,000	4,626,000	4,629,000	4,562,000	25,445,000	19,123,000	13,769,000
Provision for income taxes	2,245,000	[1]	2,442,000	2,404,000	[1]	2,189,000	2,017,000	1,635,000	1,799,000	1,734,000	9,280,000	7,185,000	5,397,000
Net Income	4,869,000	[1]	3,813,000	4,123,000	[1]	3,360,000	3,289,000	2,991,000	2,830,000	2,828,000	16,165,000	11,938,000	8,372,000
Proceeds from Life Insurance Policies											1,300,000
Earnings per share, basic (in dollars per share)	$ 0.32	[1]	$ 0.25	$ 0.27	[1]	$ 0.22	$ 0.22	$ 0.20	$ 0.19	$ 0.19	$ 1.07	$ 0.80	$ 0.57
Earnings per share, diluted (in dollars per share)	$ 0.29	[1]	$ 0.23	$ 0.25	[1]	$ 0.20	$ 0.20	$ 0.18	$ 0.17	$ 0.17	$ 0.96	$ 0.71	$ 0.52
Interest and Other Income Member [Member]
Proceeds from Life Insurance Policies	$ 800,000			$ 400,000
Earnings Per Share, Basic and Diluted (in dollars per share)	$ 0.05			$ 0.03

[1] Included in interest and other income is $0.4 million or $0.03 basic and diluted net income per share, and $0.8 million or $0.05 basic and diluted net income per share in the second and fourth quarters, respectively, for life insurance proceeds received for former Company executives that passed away during the respective quarters.