SEGMENT AND RELATED INFORMATION - Reconciliation of Operating Income from Segments to Consolidated (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated
Total segment operating income									$ 172,926	$ 156,367	$ 152,492
Total cost of revenues									(574,151)	(569,527)	(495,704)
Amortization of customer and trade name intangibles									(21,662)	(21,445)	(16,217)
Other income, net									2,116	3,471	3,378
Income before income taxes	$ 48,412	$ 49,936	$ 41,811	$ 34,883	$ 47,790	$ 40,552	$ 36,419	$ 35,077	175,042	159,838	155,870
Acquired software
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated
Total cost of revenues									(31,962)	(30,642)	(22,972)
Operating segment and corporate non-segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated
Total segment operating income									$ 226,550	$ 208,454	$ 191,681