Impact of adoption of accounting guidance on prior year’s presentation and disclosures - Effect of the Adoption of the ASU No. 2017-07 and 2016-18 (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues	[1]	$ 655,490	$ 584,855	$ 495,142
General and administrative expenses		126,909	116,202	102,515
Selling and marketing expenses		71,842	63,612	53,379
Other income, net		16,507	12,989	11,359
Operating expenses		259,403	248,436	194,443
Foreign exchange gain, interest expense and other income, net		6,647	10,549	12,309
Net cash provided by operating activities		168,420	92,435	113,159
Effect of exchange rate changes on cash, cash equivalents and restricted cash		(1,045)	(2,868)	3,935
Net increase/(decrease) in cash, cash equivalents and restricted cash		22,913	9,854	(126,117)
Cash, cash equivalents and restricted cash at the beginning of the period		104,131	94,277	220,394
Cash, cash equivalents and restricted cash at the end of the period		127,044	104,131	94,277
Previously reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues				495,586
General and administrative expenses				102,567
Selling and marketing expenses				53,383
Other income, net				11,859
ASU No. 2017-07
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Operating expenses				194,443
Foreign exchange gain, interest expense and other income, net				12,309
ASU No. 2017-07 | Previously reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Operating expenses				194,499
Foreign exchange gain, interest expense and other income, net				12,809
ASU No. 2017-07 | Effect of change increase/(decrease)
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues				(444)
General and administrative expenses				(52)
Selling and marketing expenses				(4)
Other income, net				(500)
Operating expenses				(56)
Foreign exchange gain, interest expense and other income, net				(500)
ASU No. 2016-18
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net cash provided by operating activities				113,159
Effect of exchange rate changes on cash, cash equivalents and restricted cash				3,935
Net increase/(decrease) in cash, cash equivalents and restricted cash				(126,117)
Cash, cash equivalents and restricted cash at the beginning of the period			94,277	220,394
Cash, cash equivalents and restricted cash at the end of the period				94,277
ASU No. 2016-18 | Previously reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net cash provided by operating activities				113,140
Effect of exchange rate changes on cash, cash equivalents and restricted cash				3,711
Net increase/(decrease) in cash, cash equivalents and restricted cash				(126,360)
Cash, cash equivalents and restricted cash at the beginning of the period			86,795	213,155
Cash, cash equivalents and restricted cash at the end of the period				86,795
ASU No. 2016-18 | Effect of change increase/(decrease)
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net cash provided by operating activities				19
Effect of exchange rate changes on cash, cash equivalents and restricted cash				224
Net increase/(decrease) in cash, cash equivalents and restricted cash				243
Cash, cash equivalents and restricted cash at the beginning of the period			7,482	7,239
Cash, cash equivalents and restricted cash at the end of the period				7,482
Insurance
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues		199,678	174,921	159,433
Insurance | ASU No. 2017-07
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues				159,433
Insurance | ASU No. 2017-07 | Previously reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues				159,529
Insurance | ASU No. 2017-07 | Effect of change increase/(decrease)
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues				(96)
Healthcare
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues		73,650	66,768	49,412
Healthcare | ASU No. 2017-07
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues				49,412
Healthcare | ASU No. 2017-07 | Previously reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues				49,483
Healthcare | ASU No. 2017-07 | Effect of change increase/(decrease)
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues				(71)
TT&L
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues		38,736	41,066	41,337
TT&L | ASU No. 2017-07
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues				41,337
TT&L | ASU No. 2017-07 | Previously reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues				41,409
TT&L | ASU No. 2017-07 | Effect of change increase/(decrease)
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues				(72)
F&A
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues		63,317	59,155	51,362
F&A | ASU No. 2017-07
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues				51,362
F&A | ASU No. 2017-07 | Previously reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues				51,445
F&A | ASU No. 2017-07 | Effect of change increase/(decrease)
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues				(83)
All Other
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues		48,864	58,341	56,638
All Other | ASU No. 2017-07
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues				56,638
All Other | ASU No. 2017-07 | Previously reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues				56,697
All Other | ASU No. 2017-07 | Effect of change increase/(decrease)
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues				(59)
Analytics
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues		$ 231,245	$ 184,604	136,960
Analytics | ASU No. 2017-07
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues				136,960
Analytics | ASU No. 2017-07 | Previously reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues				137,023
Analytics | ASU No. 2017-07 | Effect of change increase/(decrease)
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenues				$ (63)

[1] Exclusive of depreciation and amortization expense.