Consolidated Statements Of Income (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Consolidated Statements Of Income [Abstract]
Revenues	$ 889,065,000	$ 773,956,000	$ 692,695,000
Operating costs and expenses:
Costs of services provided	766,958,000	665,149,000	597,715,000
Selling, general and administrative	65,306,000	57,310,000	50,269,000
Other income:
Investment and interest	1,011,000	2,622,000	4,624,000
Income before income taxes	57,812,000	54,119,000	49,335,000
Income taxes	19,656,000	19,678,000	18,993,000
Net income	$ 38,156,000	$ 34,441,000	$ 30,342,000
Basic earnings per common share	$ 0.57	$ 0.52	$ 0.46
Diluted earnings per common share	$ 0.56	$ 0.51	$ 0.46
Cash dividends per common share	$ 0.63	$ 0.6	$ 0.49
Weighted average number of common shares outstanding
Basic	66,637,000	65,917,000	65,376,000
Diluted	67,585,000	67,008,000	66,429,000