Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Revenues	$ 497,774	$ 446,344
Operating expenses
Direct cost of revenues	321,117	309,072
Selling, general and administrative expenses	112,128	107,690
Amortization of other intangible assets	2,270	2,493
Operating expenses	435,515	419,255
Operating income	62,259	27,089
Other income (expense)
Interest income and other	(1,800)	605
Interest expense	(6,244)	(5,801)
Other income (expense)	(8,044)	(5,196)
Income before income tax provision	54,215	21,893
Income tax provision	15,270	7,877
Net income	$ 38,945	$ 14,016
Earnings per common share — basic (in dollars per share)	$ 1.06	$ 0.35
Earnings per common share — diluted (in dollars per share)	$ 1.04	$ 0.34
Other comprehensive income, net of tax
Foreign currency translation adjustments, net of tax expense of $0	$ 10,446	$ 7,370
Total other comprehensive income, net of tax	10,446	7,370
Comprehensive income	$ 49,391	$ 21,386