CONDENSED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Revenues	$ 632,383	$ 551,587	$ 1,283,742	$ 1,072,920
Operating expenses:
Cost of revenues (exclusive of depreciation and amortization)	419,540	355,915	843,342	700,604
Selling, general and administrative expenses	114,191	111,762	239,299	213,548
Depreciation and amortization expense	15,226	11,028	30,166	21,228
Income from operations	83,426	72,882	170,935	137,540
Interest and other income, net	1,817	1,190	4,203	4,266
Foreign exchange loss	(9,167)	(3,562)	(2,643)	(7,046)
Income before provision for income taxes	76,076	70,510	172,495	134,760
Provision for income taxes	9,452	11,733	20,306	15,229
Net income	66,624	58,777	152,189	119,531
Foreign currency translation adjustments, net of tax	12,442	2,620	(16,077)	5,563
Unrealized gain/(loss) on cash-flow hedging instruments, net of tax	6,446	1,537	(2,922)	4,637
Comprehensive income	$ 85,512	$ 62,934	$ 133,190	$ 129,731
Net income per share:
Basic (in dollars per share)	$ 1.20	$ 1.07	$ 2.74	$ 2.19
Diluted (in dollars per share)	$ 1.14	$ 1.02	$ 2.62	$ 2.08
Shares used in calculation of net income per share:
Basic (in shares)	55,700,706	54,681,959	55,493,727	54,464,753
Diluted (in shares)	58,246,231	57,614,284	58,194,401	57,426,563