CONDENSED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Revenues	$ 652,243	$ 588,103	$ 1,935,985	$ 1,661,023
Operating expenses:
Cost of revenues (exclusive of depreciation and amortization)	423,388	377,525	1,266,730	1,078,129
Selling, general and administrative expenses	116,530	118,886	355,829	332,434
Depreciation and amortization expense	15,929	11,127	46,095	32,355
Income from operations	96,396	80,565	267,331	218,105
Interest and other income, net	1,672	2,509	5,875	6,775
Foreign exchange gain/(loss)	5,896	(3,105)	3,253	(10,151)
Income before provision for income taxes	103,964	79,969	276,459	214,729
Provision for income taxes	14,532	12,967	34,838	28,196
Net income	89,432	67,002	241,621	186,533
Foreign currency translation adjustments, net of tax	199	(10,114)	(15,878)	(4,551)
Unrealized (loss)/gain on cash-flow hedging instruments, net of tax	(498)	(2,163)	(3,420)	2,474
Comprehensive income	$ 89,133	$ 54,725	$ 222,323	$ 184,456
Net income per share:
Basic (in dollars per share)	$ 1.60	$ 1.22	$ 4.34	$ 3.42
Diluted (in dollars per share)	$ 1.53	$ 1.16	$ 4.14	$ 3.24
Shares used in calculation of net income per share:
Basic (in shares)	55,883,879	54,877,666	55,624,727	54,603,903
Diluted (in shares)	58,616,106	57,844,355	58,341,178	57,567,339