Consolidated Statements Of Comprehensive Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014		Jun. 30, 2013
Income Statement [Abstract]
Revenues	$ 319,295	$ 273,604	$ 631,460		$ 547,508
Operating costs and expenses:
Costs of services provided	275,815	234,602	543,186		469,793
Selling, general and administrative	22,240	19,363	44,286		40,153
Other income:
Investment and interest	803	219	1,184		1,253
Income before income taxes	22,043	19,858	45,172		38,815
Income taxes	8,122	6,925	16,612		10,928
Net income	13,921	12,933	28,560		27,887
Per share data:
Basic earnings per common share (dollars per share)	$ 0.20	$ 0.19	$ 0.41		$ 0.41
Diluted earnings per common share (dollars per share)	$ 0.20	$ 0.19	$ 0.40		$ 0.40
Weighted average number of common shares outstanding:
Basic (shares)	70,440	68,599	70,381		68,531
Diluted (shares)	71,206	69,370	71,140		69,366
Comprehensive income:
Net income	13,921	12,933	28,560		27,887
Other comprehensive income:
Unrealized gain/(loss) on available for sale marketable securities, net of taxes	6	(106)	7	[1]	(83)
Total comprehensive income	$ 13,927	$ 12,827	$ 28,567		$ 27,804

[1] All amounts are net of tax.