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		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Revenues and cost of revenues for Company's operations management and analytics and business transformation segments [Line Items]
Revenues, net	$ 163,503	$ 122,457	$ 462,634	$ 363,992
Cost of revenues (exclusive of depreciation and amortization)	103,198	84,983	296,801	241,164
Gross profit	60,305	37,474	165,833	122,828
Operating expenses	39,556	32,083	116,368	95,853
Other income/(expense)	1,978	1,686	6,647	2,533
Income tax expense	7,565	1,002	19,309	4,523
Net income	15,162	6,075	36,803	24,985
Operations Management [Member]
Revenues and cost of revenues for Company's operations management and analytics and business transformation segments [Line Items]
Revenues, net	113,977	91,155	337,244	285,560
Cost of revenues (exclusive of depreciation and amortization)	72,032	62,870	214,032	184,263
Gross profit	41,945	28,285	123,212	101,297
Analytics and Business Transformation [Member]
Revenues and cost of revenues for Company's operations management and analytics and business transformation segments [Line Items]
Revenues, net	49,526	31,302	125,390	78,432
Cost of revenues (exclusive of depreciation and amortization)	31,166	22,113	82,769	56,901
Gross profit	$ 18,360	$ 9,189	$ 42,621	$ 21,531