Revenues and Adjusted Segment Earnings before Interest, Taxes, Depreciation and Amortization for Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenues	$ 441,920	$ 438,042	$ 460,147	$ 470,285	$ 442,204	$ 455,470	$ 449,137	$ 432,338	$ 1,810,394	$ 1,779,149	$ 1,756,212
Adjusted Segment EBITDA									285,944	283,435	291,375
Corporate Finance & Restructuring
Segment Reporting Information [Line Items]
Revenues									483,269	440,398	391,115
Adjusted Segment EBITDA									97,688	90,101	55,492
Forensic and Litigation Consulting
Segment Reporting Information [Line Items]
Revenues									457,734	482,269	483,380
Adjusted Segment EBITDA									57,882	64,267	90,468
Economic Consulting
Segment Reporting Information [Line Items]
Revenues									500,487	447,909	451,040
Adjusted Segment EBITDA									74,102	62,330	59,282
Technology
Segment Reporting Information [Line Items]
Revenues									177,720	218,599	241,310
Adjusted Segment EBITDA									25,814	39,010	63,545
Strategic Communications
Segment Reporting Information [Line Items]
Revenues									191,184	189,974	189,367
Adjusted Segment EBITDA									$ 30,458	$ 27,727	$ 22,588