Segment Reporting - Revenues and Adjusted Segment Earnings before Interest, Taxes, Depreciation and Amortization for Reportable Segments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Revenues	$ 2,776,222	$ 2,461,275	$ 2,352,717
Adjusted Segment EBITDA	455,265	423,624	439,514
Corporate Finance
Segment Reporting Information [Line Items]
Revenues	938,969	910,184	723,721
Adjusted Segment EBITDA	155,482	216,830	160,735
FLC
Segment Reporting Information [Line Items]
Revenues	584,835	500,275	577,780
Adjusted Segment EBITDA	72,545	33,374	104,435
Economic Consulting
Segment Reporting Information [Line Items]
Revenues	697,405	599,088	592,542
Adjusted Segment EBITDA	117,186	91,432	84,112
Technology
Segment Reporting Information [Line Items]
Revenues	287,366	223,016	215,584
Adjusted Segment EBITDA	55,739	43,013	45,688
Strategic Communications
Segment Reporting Information [Line Items]
Revenues	267,647	228,712	243,090
Adjusted Segment EBITDA	$ 54,313	$ 38,975	$ 44,544