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, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Revenues	$ 442,204	$ 455,470	$ 449,137	$ 432,338	$ 425,158	$ 451,178	$ 454,324	$ 425,552	$ 1,779,149	$ 1,756,212	$ 1,652,432
Adjusted Segment EBITDA									283,435	291,375	313,260
Corporate Finance & Restructuring
Segment Reporting Information [Line Items]
Revenues									440,398	391,115	382,526
Adjusted Segment EBITDA									90,101	55,492	67,183
Forensic and Litigation Consulting
Segment Reporting Information [Line Items]
Revenues									482,269	483,380	433,632
Adjusted Segment EBITDA									64,267	90,468	74,481
Economic Consulting
Segment Reporting Information [Line Items]
Revenues									447,909	451,040	447,366
Adjusted Segment EBITDA									62,330	59,282	92,204
Technology
Segment Reporting Information [Line Items]
Revenues									218,599	241,310	202,663
Adjusted Segment EBITDA									39,010	63,545	60,655
Strategic Communications
Segment Reporting Information [Line Items]
Revenues									189,974	189,367	186,245
Adjusted Segment EBITDA									$ 27,727	$ 22,588	$ 18,737