Segment and Geographical Information - Revenues and Cost of Revenues for Company's Reportable Segments (Details) $ in Thousands		3 Months Ended
		Mar. 31, 2019 USD ($) operating_segment	Mar. 31, 2018 USD ($)
Revenues and cost of revenues for Company's reportable segments [Line Items]
Revenues, net		$ 239,573	$ 206,973
Cost of revenues	[1]	157,240	138,101
Gross profit	[1]	82,333	68,872
Operating expenses		65,472	53,722
Foreign exchange gain, interest expense and other income, net		2,101	3,611
Income tax expense/(benefit)		4,200	(4,453)
Loss from equity-method investment		67	56
Net income attributable to ExlService Holdings, Inc. stockholders		$ 14,695	23,158
Number of operating segments, industry focused | operating_segment		5
Number of capability operating segments | operating_segment		1
BPM and related services
Revenues and cost of revenues for Company's reportable segments [Line Items]
Revenues, net		$ 152,612	149,871
Analytics services
Revenues and cost of revenues for Company's reportable segments [Line Items]
Revenues, net		86,961	57,102
Insurance
Revenues and cost of revenues for Company's reportable segments [Line Items]
Revenues, net		69,038	63,903
Cost of revenues		46,692	42,427
Gross profit		22,346	21,476
Healthcare
Revenues and cost of revenues for Company's reportable segments [Line Items]
Revenues, net		20,569	22,797
Cost of revenues		16,995	17,242
Gross profit		3,574	5,555
TT&L
Revenues and cost of revenues for Company's reportable segments [Line Items]
Revenues, net		17,425	17,499
Cost of revenues		9,800	10,443
Gross profit		7,625	7,056
F&A
Revenues and cost of revenues for Company's reportable segments [Line Items]
Revenues, net		25,724	23,972
Cost of revenues		14,274	14,729
Gross profit		11,450	9,243
All Other
Revenues and cost of revenues for Company's reportable segments [Line Items]
Revenues, net		19,856	21,700
Cost of revenues		12,577	15,185
Gross profit		7,279	6,515
Analytics
Revenues and cost of revenues for Company's reportable segments [Line Items]
Revenues, net		86,961	57,102
Cost of revenues		56,902	38,075
Gross profit		$ 30,059	$ 19,027

[1] Exclusive of depreciation and amortization.