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, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Revenues	$ 460,147	$ 449,137	$ 930,432	$ 881,475
Adjusted Segment EBITDA	76,087	75,100	162,748	147,032
Corporate Finance & Restructuring
Segment Reporting Information [Line Items]
Revenues	132,142	109,113	259,298	215,325
Adjusted Segment EBITDA	32,041	22,032	63,644	44,512
Forensic and Litigation Consulting
Segment Reporting Information [Line Items]
Revenues	118,193	126,131	237,197	249,396
Adjusted Segment EBITDA	15,190	19,979	34,998	42,050
Economic Consulting
Segment Reporting Information [Line Items]
Revenues	118,006	108,698	248,737	214,779
Adjusted Segment EBITDA	15,381	15,292	36,700	26,848
Technology
Segment Reporting Information [Line Items]
Revenues	41,882	61,826	90,163	116,480
Adjusted Segment EBITDA	5,035	12,166	12,858	22,239
Strategic Communications
Segment Reporting Information [Line Items]
Revenues	49,924	43,369	95,037	85,495
Adjusted Segment EBITDA	$ 8,440	$ 5,631	$ 14,548	$ 11,383