Segment Information - Revenues and Cost of Revenues for Company's Operations Management and Analytics and Business Transformation Segments (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues and cost of revenues for Company's outsourcing services and transformation services segments [Line Items]
Revenues, net	$ 165,858	$ 163,503	$ 155,621	$ 143,510	$ 135,286	$ 122,457	$ 119,738	$ 121,797	$ 628,492	$ 499,278	$ 478,452
Cost of revenues (exclusive of depreciation and amortization)									402,917	332,535	290,942
Gross profit	59,742	60,305	55,143	50,385	43,915	37,474	38,479	46,875	225,575	166,743	187,510
Operating expenses									158,232	132,703	120,090
Foreign exchange gain/(loss) and other income, net									8,433	3,598	(2,443)
Income tax expense									24,211	5,193	16,880
Net income	14,762	15,162	12,074	9,567	7,461	6,075	7,762	11,147	51,565	32,445	48,097
Operations Management
Revenues and cost of revenues for Company's outsourcing services and transformation services segments [Line Items]
Revenues, net	129,397	128,043	125,048	123,853	116,292	104,511	104,614	108,246	506,341	433,663	432,916
Cost of revenues (exclusive of depreciation and amortization)									324,079	286,493	260,241
Gross profit	47,333	46,566	44,239	44,124	38,075	32,651	34,151	42,293	182,262	147,170	172,675
Analytics
Revenues and cost of revenues for Company's outsourcing services and transformation services segments [Line Items]
Revenues, net	36,461	35,460	30,573	19,657	18,994	17,946	15,124	13,551	122,151	65,615	45,536
Cost of revenues (exclusive of depreciation and amortization)									78,838	46,042	30,701
Gross profit	$ 12,409	$ 13,739	$ 10,904	$ 6,261	$ 5,840	$ 4,823	$ 4,328	$ 4,582	$ 43,313	$ 19,573	$ 14,835