Segments and Geographic Information - Operation by Delivery Location (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Revenue	$ 1,710,261	$ 1,614,762	$ 1,625,687
Americas [Member]
Segment Reporting Information [Line Items]
Revenue	1,381,008	1,296,660	1,330,638
Americas [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue	1,381,008	1,296,660	1,330,638
Americas [Member] | Operating Segments [Member] | United States [Member]
Segment Reporting Information [Line Items]
Revenue	647,497	614,493	668,580
Americas [Member] | Operating Segments [Member] | The Philippines [Member]
Segment Reporting Information [Line Items]
Revenue	267,965	250,888	231,966
Americas [Member] | Operating Segments [Member] | Costa Rica [Member]
Segment Reporting Information [Line Items]
Revenue	151,753	127,078	127,963
Americas [Member] | Operating Segments [Member] | Canada [Member]
Segment Reporting Information [Line Items]
Revenue	102,714	99,037	102,353
Americas [Member] | Operating Segments [Member] | El Salvador [Member]
Segment Reporting Information [Line Items]
Revenue	71,591	81,195	81,156
Americas [Member] | Operating Segments [Member] | Other [Member]
Segment Reporting Information [Line Items]
Revenue	139,488	123,969	118,620
EMEA [Member]
Segment Reporting Information [Line Items]
Revenue	329,238	318,013	294,954
EMEA [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue	329,238	318,013	294,954
EMEA [Member] | Operating Segments [Member] | Other [Member]
Segment Reporting Information [Line Items]
Revenue	227,370	223,847	203,251
EMEA [Member] | Operating Segments [Member] | Germany [Member]
Segment Reporting Information [Line Items]
Revenue	101,868	94,166	91,703
Other Segment [Member]
Segment Reporting Information [Line Items]
Revenue	$ 15	$ 89	$ 95