CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Revenues	$ 2,065,008	$ 1,724,741	$ 1,523,101
Costs of services	1,386,263	1,167,306	1,068,226
Gross profit	678,745	557,435	454,875
Selling, general and administrative expenses	492,170	397,523	317,345
Amortization of intangible assets	34,467	22,130	20,943
Operating income	152,108	137,782	116,587
Interest expense, net	(26,444)	(12,730)	(13,931)
Write-off of loan costs	(3,751)	0	(14,958)
Income before income taxes	121,913	125,052	87,698
Provision for income taxes	50,491	51,557	36,558
Income from continuing operations	71,422	73,495	51,140
Gain on sale of discontinued operations, net of income taxes	25,703	0	30,840
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	525	3,689	2,532
Net income	$ 97,650	$ 77,184	$ 84,512
Basic earnings per common share:
Continuing operations	$ 1.37	$ 1.38	$ 0.96
Discontinued operations	0.50	0.06	0.62
Net income	1.87	1.44	1.58
Diluted earnings per common share:
Continuing operations	1.35	1.35	0.94
Discontinued operations	0.49	0.07	0.61
Net income	$ 1.84	$ 1.42	$ 1.55
Number of shares and share equivalents used to calculate earnings per share:
Basic (in shares)	52,259	53,437	53,481
Diluted (in shares)	53,005	54,294	54,555
Reconciliation of net income to comprehensive income:
Net income	$ 97,650	$ 77,184	$ 84,512
Changes in fair value of derivative, net of tax	122	86	193
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	(3,714)	(4,772)	1,128
Comprehensive income	$ 94,058	$ 72,498	$ 85,833