Segment & Geographical Information - Revenues and Cost of Revenues for Company's Reportable Segments (Detail) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) operating_segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Revenues and cost of revenues for Company's reportable segments [Line Items]
Revenues, net	$ 197,875	$ 192,345	$ 189,057	$ 183,033	$ 177,274	$ 171,200	$ 170,478	$ 167,036	$ 762,310	$ 685,988	$ 628,492
Cost of revenues (exclusive of depreciation and amortization)									495,586	447,956	402,917
Gross profit	68,506	69,156	65,211	63,851	61,490	59,433	58,452	58,657	266,724	238,032	225,575
Operating expenses									194,499	173,810	158,232
Foreign exchange gain, interest expense and other income, net									12,809	19,662	8,433
Income tax expense									36,146	22,151	24,211
Net income	$ (9,355)	$ 21,077	$ 20,378	$ 16,788	$ 15,488	$ 16,050	$ 16,375	$ 13,820	$ 48,888	61,733	51,565
Number of operating segments, industry focused | operating_segment									5
Number of operating segments, finance and accounting | operating_segment									1
BPM and related services
Revenues and cost of revenues for Company's reportable segments [Line Items]
Revenues, net									$ 552,367	520,254	506,341
Analytics services
Revenues and cost of revenues for Company's reportable segments [Line Items]
Revenues, net									209,943	165,734	122,151
Insurance
Revenues and cost of revenues for Company's reportable segments [Line Items]
Revenues, net									234,794	206,327	199,878
Cost of revenues (exclusive of depreciation and amortization)									159,529	146,203	134,196
Gross profit									75,265	60,124	65,682
Healthcare
Revenues and cost of revenues for Company's reportable segments [Line Items]
Revenues, net									77,013	68,656	55,209
Cost of revenues (exclusive of depreciation and amortization)									49,483	44,098	37,224
Gross profit									27,530	24,558	17,985
TT&L
Revenues and cost of revenues for Company's reportable segments [Line Items]
Revenues, net									70,951	69,366	62,264
Cost of revenues (exclusive of depreciation and amortization)									41,409	41,962	37,506
Gross profit									29,542	27,404	24,758
F&A
Revenues and cost of revenues for Company's reportable segments [Line Items]
Revenues, net									86,527	79,416	78,504
Cost of revenues (exclusive of depreciation and amortization)									51,445	48,302	46,846
Gross profit									35,082	31,114	31,658
All Other
Revenues and cost of revenues for Company's reportable segments [Line Items]
Revenues, net									83,082	96,489	110,486
Cost of revenues (exclusive of depreciation and amortization)									56,697	61,050	68,307
Gross profit									26,385	35,439	42,179
Analytics
Revenues and cost of revenues for Company's reportable segments [Line Items]
Revenues, net									209,943	165,734	122,151
Cost of revenues (exclusive of depreciation and amortization)									137,023	106,341	78,838
Gross profit									$ 72,920	$ 59,393	$ 43,313