Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerators:
Net income	$ 21,356	$ 19,044	$ 12,564	$ 14,695	$ 3,857	$ 15,249	$ 14,462	$ 23,158	$ 67,659	$ 56,726	$ 48,888
Denominators:
Basic weighted average common shares outstanding (in shares)	34,253,308	34,322,449	34,451,671	34,374,815	34,388,025	34,458,520	34,511,777	34,446,265	34,350,150	34,451,008	33,897,916
Dilutive effect of share based awards (in shares)									382,533	579,976	1,212,294
Diluted weighted average common shares outstanding (in shares)	34,696,896	34,699,497	34,702,547	34,833,435	34,921,388	35,207,991	35,142,388	35,302,926	34,732,683	35,030,984	35,110,210
Earnings per share attributable to ExlService Holdings Inc. stockholders:
Basic (in dollars per share)	$ 0.62	$ 0.55	$ 0.36	$ 0.43	$ 0.11	$ 0.44	$ 0.42	$ 0.67	$ 1.97	$ 1.65	$ 1.44
Diluted (in dollars per share)	$ 0.62	$ 0.55	$ 0.36	$ 0.42	$ 0.11	$ 0.43	$ 0.41	$ 0.66	$ 1.95	$ 1.62	$ 1.39
Weighted average potentially dilutive shares considered anti-dilutive and not included in computing diluted earnings per share (in shares)									106,375	121,344	151,961