Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income Statement [Abstract]
Revenues	$ 460,147	$ 449,137	$ 930,432	$ 881,475
Operating expenses
Direct cost of revenues	303,194	291,469	608,830	570,499
Selling, general and administrative expenses	108,245	109,045	211,854	211,259
Special charges	1,750		6,811
Acquisition-related contingent consideration	206	(1,538)	1,340	(1,304)
Amortization of other intangible assets	2,590	3,007	5,196	6,019
Costs and Expenses, Total	415,985	401,983	834,031	786,473
Operating income	44,162	47,154	96,401	95,002
Other income (expense)
Interest income and other	4,125	950	6,682	813
Interest expense	(6,303)	(12,473)	(12,532)	(24,841)
Other (expense) income	(2,178)	(11,523)	(5,850)	(24,028)
Income before income tax provision	41,984	35,631	90,551	70,974
Income tax provision	15,437	13,922	33,823	25,579
Net income	$ 26,547	$ 21,709	$ 56,728	$ 45,395
Earnings per common share — basic	$ 0.65	$ 0.53	$ 1.40	$ 1.12
Earnings per common share — diluted	$ 0.64	$ 0.52	$ 1.37	$ 1.09
Other comprehensive (loss) income, net of tax
Foreign currency translation adjustments, net of tax expense of $0	$ (18,809)	$ 13,298	$ (19,167)	$ (7,184)
Total other comprehensive (loss) income, net of tax	(18,809)	13,298	(19,167)	(7,184)
Comprehensive income	$ 7,738	$ 35,007	$ 37,561	$ 38,211