SEGMENT AND GEOGRAPHIC DISCLOSURES - Geographic Breakdown of Revenues and Total Long-Lived Assets (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
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues		$ 207,303	$ 219,093	$ 189,304	$ 236,839	$ 287,807	$ 290,079	$ 315,829	$ 269,599	$ 852,539	[1]	$ 1,163,314	[1]	$ 1,246,929	[1]
Total Long-Lived Assets	[2]	337,460				376,018				337,460		376,018		326,166
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues	[1]									606,818		838,385		908,382
Total Long-Lived Assets	[2]	289,507				328,832				289,507		328,832		298,567
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues	[1]									87,028		127,574		139,900
Total Long-Lived Assets	[2]	8,291				8,625				8,291		8,625		4,165
Europe
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues	[1]									104,667		126,794		126,142
Total Long-Lived Assets	[2]	34,674				32,517				34,674		32,517		20,224
Other foreign countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues	[1]									54,026		70,561		72,505
Total Long-Lived Assets	[2]	$ 4,988				$ 6,044				$ 4,988		$ 6,044		$ 3,210

[1] Revenues attributable to individual countries/geographic areas are based on the country of domicile of the legal entity that performs the work.

[2] Excludes goodwill, intangible assets not being amortized that are to be held and used, financial instruments and deferred tax assets.