CONDENSED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Statement [Abstract]
Revenues	$ 651,359	$ 521,333
Operating expenses:
Cost of revenues (exclusive of depreciation and amortization)	423,802	344,689
Selling, general and administrative expenses	125,108	101,786
Depreciation and amortization expense	14,940	10,200
Income from operations	87,509	64,658
Interest and other income, net	2,386	3,076
Foreign exchange gain/(loss)	6,524	(3,484)
Income before provision for income taxes	96,419	64,250
Provision for income taxes	10,854	3,496
Net income	85,565	60,754
Foreign currency translation adjustments, net of tax	(28,519)	2,943
Unrealized (loss)/gain on cash-flow hedging instruments, net of tax	(9,368)	3,100
Comprehensive income	$ 47,678	$ 66,797
Net income per share:
Basic (in dollars per share)	$ 1.55	$ 1.12
Diluted (in dollars per share)	$ 1.47	$ 1.06
Shares used in calculation of net income per share:
Basic (in shares)	55,286,747	54,245,133
Diluted (in shares)	58,142,570	57,236,427