Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Income Statement [Abstract]
Revenues	$ 384,807	$ 355,246
Operating costs and expenses:
Costs of services provided	330,044	303,936
Selling, general and administrative expense	25,346	26,763
Other income, net:
Investment and interest	187	507
Income before income taxes	29,604	25,054
Income tax provision	10,978	9,538
Net income	$ 18,626	$ 15,516
Per share data:
Basic earnings per common share (dollars per share)	$ 0.26	$ 0.22
Diluted earnings per common share (dollars per share)	$ 0.26	$ 0.22
Weighted average number of common shares outstanding:
Basic (shares)	72,364	71,469
Diluted (shares)	73,014	72,159
Comprehensive income:
Net income	$ 18,626	$ 15,516
Other comprehensive income:
Unrealized gain on available for sale marketable securities, net of taxes	555	3
Total comprehensive income	$ 19,181	$ 15,519