Consolidated Statements Of Comprehensive Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013		Jun. 30, 2012
Income Statement [Abstract]
Revenues	$ 273,604	$ 267,108	$ 547,508		$ 527,715
Operating costs and expenses:
Costs of services provided	234,602	230,206	469,793		457,701
Selling, general and administrative	19,363	18,524	40,153		39,506
Other income:
Investment and interest	219	(95)	1,253		1,558
Income before income taxes	19,858	18,283	38,815		32,066
Income taxes	6,925	6,963	10,928		12,167
Net income	12,933	11,320	27,887		19,899
Per share data:
Basic earnings per common share (dollars per share)	$ 0.19	$ 0.17	$ 0.41		$ 0.30
Diluted earnings per common share (dollars per share)	$ 0.19	$ 0.17	$ 0.40		$ 0.29
Weighted average number of common shares outstanding:
Basic (shares)	68,599	67,296	68,531		67,189
Diluted (shares)	69,370	68,228	69,366		68,155
Comprehensive income:
Net income	12,933	11,320	27,887		19,899
Other comprehensive income:
Unrealized loss on available for sale marketable securities, net of taxes	(106)	(17)	(83)	[1]	(190)
Total comprehensive income	$ 12,827	$ 11,303	$ 27,804		$ 19,709

[1] All amounts are net of tax.