Consolidated Statements Of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Revenues	$ 1,436,849	$ 1,293,183	$ 1,149,890
Operating costs and expenses:
Costs of services provided	1,236,108	1,155,293	995,104
Selling, general and administrative	111,689	107,810	91,998
Other income:
Investment and interest	712	1,628	3,701
Income before income taxes	89,764	31,708	66,489
Income taxes	31,740	9,858	19,360
Net income	$ 58,024	$ 21,850	$ 47,129
Per share data:
Basic earnings per common share (in dollars per share)	$ 0.81	$ 0.31	$ 0.68
Diluted earnings per common share (in dollars per share)	$ 0.80	$ 0.31	$ 0.67
Weighted average number of common shares outstanding:
Basic (in shares)	71,826	70,616	69,206
Diluted (in shares)	72,512	71,341	70,045
Comprehensive income:
Net income	$ 58,024	$ 21,850	$ 47,129
Other comprehensive income:
Unrealized gain (loss) on available for sale marketable securities, net of taxes	518	(24)	(78)
Total comprehensive income	$ 58,542	$ 21,826	$ 47,051