Revenues and Adjusted Segment Earnings before Interest, Taxes, Depreciation and Amortization for Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Revenues	$ 448,962	$ 438,042	$ 1,340,021	$ 1,368,474
Adjusted Segment EBITDA	75,380	67,577	190,283	230,325
Corporate Finance & Restructuring
Segment Reporting Information [Line Items]
Revenues	128,121	110,617	351,509	369,915
Adjusted Segment EBITDA	26,734	17,762	57,107	81,406
Forensic and Litigation Consulting
Segment Reporting Information [Line Items]
Revenues	118,639	115,045	341,455	352,242
Adjusted Segment EBITDA	22,539	16,554	49,092	51,552
Economic Consulting
Segment Reporting Information [Line Items]
Revenues	111,753	122,480	374,978	371,217
Adjusted Segment EBITDA	12,061	18,354	47,680	55,054
Technology
Segment Reporting Information [Line Items]
Revenues	42,282	44,072	133,935	134,235
Adjusted Segment EBITDA	5,973	7,398	19,198	20,256
Strategic Communications
Segment Reporting Information [Line Items]
Revenues	48,167	45,828	138,144	140,865
Adjusted Segment EBITDA	$ 8,073	$ 7,509	$ 17,206	$ 22,057