Special Charges By Segment (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Special Charges [Line Items]
Segment special charges			$ 26,830,000	$ 6,811,000
Special charges	$ 0	$ 0	30,074,000	6,811,000
Operating Segments
Special Charges [Line Items]
Segment special charges			26,830,000	6,811,000
Operating Segments | Corporate Finance & Restructuring
Special Charges [Line Items]
Segment special charges			3,049,000
Operating Segments | Forensic and Litigation Consulting
Special Charges [Line Items]
Segment special charges			10,445,000	1,750,000
Operating Segments | Economic Consulting
Special Charges [Line Items]
Segment special charges			5,910,000
Operating Segments | Technology
Special Charges [Line Items]
Segment special charges			3,827,000	$ 5,061,000
Operating Segments | Strategic Communications
Special Charges [Line Items]
Segment special charges			3,599,000
Unallocated Corporate
Special Charges [Line Items]
Special charges			$ 3,244,000