Consolidated Statements of Comprehensive Income (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Revenues	$ 272,681,000	$ 218,929,000	$ 800,396,000	$ 638,826,000
Operating costs and expenses:
Costs of services provided	234,281,000	188,041,000	691,982,000	549,768,000
Selling, general and administrative	20,789,000	14,344,000	60,295,000	46,635,000
Other income (loss):
Investment and interest	962,000	(1,355,000)	2,520,000	(178,000)
Income before income taxes	18,573,000	15,189,000	50,639,000	42,245,000
Income taxes	7,056,000	5,193,000	19,223,000	14,654,000
Net income	11,517,000	9,996,000	31,416,000	27,591,000
Per share data:
Basic earnings per common share	$ 0.17	$ 0.15	$ 0.47	$ 0.41
Diluted earnings per common share	$ 0.17	$ 0.15	$ 0.46	$ 0.41
Cash dividends per common share	$ 0.16	$ 0.16	$ 0.49	$ 0.47
Weighted average number of common shares outstanding:
Basic	67,651,000	66,710,000	67,344,000	66,544,000
Diluted	68,635,000	67,530,000	68,316,000	67,510,000
Comprehensive income:
Net income	11,517,000	9,996,000	31,416,000	27,591,000
Other comprehensive income:
Unrealized gain/(loss) on available for sale marketable securities, net of taxes	18,000	76,000	(172,000)	451,000
Total comprehensive income	$ 11,535,000	$ 10,072,000	$ 31,244,000	$ 28,042,000