Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Numerator:
Net income	$ 3,857	$ 15,249	$ 14,462	$ 23,158	$ (9,355)	$ 21,077	$ 20,378	$ 16,788	$ 56,726	$ 48,888	[1],[2]	$ 61,733	[1],[2]
Denominators:
Basic weighted average common shares outstanding (in shares)	34,388,025	34,458,520	34,511,777	34,446,265	34,086,711	33,838,374	33,819,320	33,845,560	34,451,008	33,897,916	[2]	33,566,367	[2]
Dilutive effect of share based awards (in shares)									579,976	1,212,294		996,952
Diluted weighted average common shares outstanding (in shares)	34,921,388	35,207,991	35,142,388	35,302,926	34,086,711	35,043,987	34,993,226	35,108,882	35,030,984	35,110,210	[2]	34,563,319	[2]
Earnings per share attributable to ExlService Holdings, Inc. stockholders:
Basic (in dollars per share)	$ 0.11	$ 0.44	$ 0.42	$ 0.67	$ (0.27)	$ 0.62	$ 0.60	$ 0.50	$ 1.65	$ 1.44	[2]	$ 1.84	[2]
Diluted (in dollars per share)	$ 0.11	$ 0.43	$ 0.41	$ 0.66	$ (0.27)	$ 0.60	$ 0.58	$ 0.48	$ 1.62	$ 1.39	[2]	$ 1.79	[2]
Weighted average potentially dilutive shares considered anti-dilutive and not included in computing diluted earnings per share (in shares)									121,344	151,961		92,538

[1] Adjusted pursuant to adoption of ASU 2016-18, Statements of Cash Flows, Restricted Cash. Refer to Note 8 and Note 27 to the consolidated financial statements.

[2] Adjusted pursuant to adoption of ASU No. 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Post-retirement Benefit Cost. Refer to Note 21 and Note 27 to the consolidated financial statements.