Revenues and Adjusted Segment Earnings before Interest, Taxes, Depreciation and Amortization for Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Revenues	$ 444,715	$ 460,147	$ 891,059	$ 930,432
Adjusted Segment EBITDA	58,886	76,087	114,903	162,748
Corporate Finance & Restructuring
Segment Reporting Information [Line Items]
Revenues	117,487	132,142	223,388	259,298
Adjusted Segment EBITDA	20,048	32,041	30,373	63,644
Forensic and Litigation Consulting
Segment Reporting Information [Line Items]
Revenues	111,410	118,193	222,816	237,197
Adjusted Segment EBITDA	13,032	15,190	26,553	34,998
Economic Consulting
Segment Reporting Information [Line Items]
Revenues	124,004	118,006	263,225	248,737
Adjusted Segment EBITDA	15,509	15,381	35,619	36,700
Technology
Segment Reporting Information [Line Items]
Revenues	45,566	41,882	91,653	90,163
Adjusted Segment EBITDA	5,421	5,035	13,225	12,858
Strategic Communications
Segment Reporting Information [Line Items]
Revenues	46,248	49,924	89,977	95,037
Adjusted Segment EBITDA	$ 4,876	$ 8,440	$ 9,133	$ 14,548