Supplemental Condensed Consolidating Guarantor and Non-Guarantor Financial Information (Condensed Consolidating Statement Of Comprehensive Income (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenues	$ 448,962,000	$ 438,042,000	$ 1,340,021,000	$ 1,368,474,000
Operating expenses
Direct cost of revenues	294,851,000	293,702,000	907,994,000	902,532,000
Selling, general and administrative expenses	103,909,000	106,220,000	318,546,000	318,074,000
Special charges	0	0	30,074,000	6,811,000
Acquisition-related contingent consideration	252,000	201,000	1,424,000	1,541,000
Amortization of other intangible assets	2,882,000	2,845,000	7,797,000	8,041,000
Costs and Expenses, Total	401,894,000	402,968,000	1,265,835,000	1,236,999,000
Operating income	47,068,000	35,074,000	74,186,000	131,475,000
Other income (expense)	(5,657,000)	(3,091,000)	(15,511,000)	(8,941,000)
Income before income tax provision	41,411,000	31,983,000	58,675,000	122,534,000
Income tax provision	9,197,000	10,292,000	17,601,000	44,115,000
Net income	32,214,000	21,691,000	41,074,000	78,419,000
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments, net of tax expense of $0	11,234,000	(4,478,000)	28,778,000	(23,645,000)
Total other comprehensive income (loss), net of tax	11,234,000	(4,478,000)	28,778,000	(23,645,000)
Comprehensive income	43,448,000	17,213,000	69,852,000	54,774,000
Reportable Legal Entities | FTI Consulting
Revenues	163,311,000	159,431,000	478,767,000	517,703,000
Operating expenses
Direct cost of revenues	105,857,000	107,579,000	325,560,000	337,262,000
Selling, general and administrative expenses	44,781,000	47,388,000	136,487,000	138,038,000
Special charges			13,592,000	1,750,000
Acquisition-related contingent consideration				6,000
Amortization of other intangible assets	1,304,000	986,000	3,089,000	2,958,000
Costs and Expenses, Total	151,942,000	155,953,000	478,728,000	480,014,000
Operating income	11,369,000	3,478,000	39,000	37,689,000
Other income (expense)	(5,912,000)	(6,913,000)	(16,525,000)	(18,882,000)
Income before income tax provision	5,457,000	(3,435,000)	(16,486,000)	18,807,000
Income tax provision	4,438,000	(1,402,000)	(8,179,000)	9,781,000
Equity in net earnings of subsidiaries	31,195,000	23,724,000	49,381,000	69,393,000
Net income	32,214,000	21,691,000	41,074,000	78,419,000
Other comprehensive income (loss), net of tax:
Comprehensive income	32,214,000	21,691,000	41,074,000	78,419,000
Reportable Legal Entities | Guarantor Subsidiaries
Revenues	136,827,000	153,986,000	459,569,000	463,152,000
Operating expenses
Direct cost of revenues	95,432,000	104,109,000	321,606,000	312,921,000
Selling, general and administrative expenses	30,280,000	30,704,000	92,217,000	92,490,000
Special charges			7,306,000	4,563,000
Acquisition-related contingent consideration	252,000	201,000	1,424,000	1,535,000
Amortization of other intangible assets	541,000	541,000	1,621,000	1,639,000
Costs and Expenses, Total	126,505,000	135,555,000	424,174,000	413,148,000
Operating income	10,322,000	18,431,000	35,395,000	50,004,000
Other income (expense)	(4,548,000)	(794,000)	(5,046,000)	(3,063,000)
Income before income tax provision	5,774,000	17,637,000	30,349,000	46,941,000
Income tax provision	2,260,000	8,194,000	17,397,000	21,918,000
Equity in net earnings of subsidiaries	21,731,000	11,878,000	26,442,000	38,867,000
Net income	25,245,000	21,321,000	39,394,000	63,890,000
Other comprehensive income (loss), net of tax:
Comprehensive income	25,245,000	21,321,000	39,394,000	63,890,000
Reportable Legal Entities | Non-Guarantor Subsidiaries
Revenues	151,197,000	126,995,000	408,780,000	394,618,000
Operating expenses
Direct cost of revenues	95,874,000	84,313,000	267,742,000	259,184,000
Selling, general and administrative expenses	28,909,000	28,199,000	90,023,000	87,710,000
Special charges			9,176,000	498,000
Amortization of other intangible assets	1,795,000	1,823,000	5,306,000	5,584,000
Costs and Expenses, Total	126,578,000	114,335,000	372,247,000	352,976,000
Operating income	24,619,000	12,660,000	36,533,000	41,642,000
Other income (expense)	4,803,000	4,616,000	6,060,000	13,004,000
Income before income tax provision	29,422,000	17,276,000	42,593,000	54,646,000
Income tax provision	2,499,000	3,500,000	8,383,000	12,416,000
Net income	26,923,000	13,776,000	34,210,000	42,230,000
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments, net of tax expense of $0	11,234,000	(4,478,000)	28,778,000	(23,645,000)
Total other comprehensive income (loss), net of tax	11,234,000	(4,478,000)	28,778,000	(23,645,000)
Comprehensive income	38,157,000	9,298,000	62,988,000	18,585,000
Eliminations
Revenues	(2,373,000)	(2,370,000)	(7,095,000)	(6,999,000)
Operating expenses
Direct cost of revenues	(2,312,000)	(2,299,000)	(6,914,000)	(6,835,000)
Selling, general and administrative expenses	(61,000)	(71,000)	(181,000)	(164,000)
Amortization of other intangible assets	(758,000)	(505,000)	(2,219,000)	(2,140,000)
Costs and Expenses, Total	(3,131,000)	(2,875,000)	(9,314,000)	(9,139,000)
Operating income	758,000	505,000	2,219,000	2,140,000
Income before income tax provision	758,000	505,000	2,219,000	2,140,000
Equity in net earnings of subsidiaries	(52,926,000)	(35,602,000)	(75,823,000)	(108,260,000)
Net income	(52,168,000)	(35,097,000)	(73,604,000)	(106,120,000)
Other comprehensive income (loss), net of tax:
Comprehensive income	$ (52,168,000)	$ (35,097,000)	$ (73,604,000)	$ (106,120,000)