Supplemental Condensed Consolidating Guarantor and Non-Guarantor Financial Information - Condensed Consolidating Statement Of Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues	$ 497,774	$ 446,344
Operating expenses
Direct cost of revenues	321,117	309,072
Selling, general and administrative expenses	112,128	107,690
Amortization of other intangible assets	2,270	2,493
Operating expenses	435,515	419,255
Operating income	62,259	27,089
Other income (expense)	(8,044)	(5,196)
Income before income tax provision	54,215	21,893
Income tax provision	15,270	7,877
Equity in net earnings of subsidiaries	0	0
Net income	38,945	14,016
Other comprehensive income, net of tax:
Foreign currency translation adjustments, net of tax expense of $0	10,446	7,370
Total other comprehensive income, net of tax	10,446	7,370
Comprehensive income	49,391	21,386
Foreign currency translation adjustments, tax expense	0	0
Eliminations
Revenues	(2,448)	(2,592)
Operating expenses
Direct cost of revenues	(2,338)	(2,533)
Selling, general and administrative expenses	(110)	(59)
Amortization of other intangible assets	(808)	(719)
Operating expenses	(3,256)	(3,311)
Operating income	808	719
Other income (expense)	(23,000)	0
Income before income tax provision	(22,192)	719
Income tax provision	0	0
Equity in net earnings of subsidiaries	(42,867)	(28,409)
Net income	(65,059)	(27,690)
Other comprehensive income, net of tax:
Foreign currency translation adjustments, net of tax expense of $0	0	0
Total other comprehensive income, net of tax	0	0
Comprehensive income	(65,059)	(27,690)
FTI Consulting
Revenues	185,321	151,807
Operating expenses
Direct cost of revenues	115,460	111,258
Selling, general and administrative expenses	50,681	45,798
Amortization of other intangible assets	874	902
Operating expenses	167,015	157,958
Operating income	18,306	(6,151)
Other income (expense)	16,930	(5,252)
Income before income tax provision	35,236	(11,403)
Income tax provision	4,370	(5,583)
Equity in net earnings of subsidiaries	8,079	19,836
Net income	38,945	14,016
Other comprehensive income, net of tax:
Foreign currency translation adjustments, net of tax expense of $0	0	0
Total other comprehensive income, net of tax	0	0
Comprehensive income	38,945	14,016
Guarantor Subsidiaries
Revenues	157,129	171,026
Operating expenses
Direct cost of revenues	109,398	117,786
Selling, general and administrative expenses	28,980	31,379
Amortization of other intangible assets	414	540
Operating expenses	138,792	149,705
Operating income	18,337	21,321
Other income (expense)	(309)	(427)
Income before income tax provision	18,028	20,894
Income tax provision	6,040	10,918
Equity in net earnings of subsidiaries	34,788	8,573
Net income	46,776	18,549
Other comprehensive income, net of tax:
Foreign currency translation adjustments, net of tax expense of $0	0	0
Total other comprehensive income, net of tax	0	0
Comprehensive income	46,776	18,549
Non-Guarantor Subsidiaries
Revenues	157,772	126,103
Operating expenses
Direct cost of revenues	98,597	82,561
Selling, general and administrative expenses	32,577	30,572
Amortization of other intangible assets	1,790	1,770
Operating expenses	132,964	114,903
Operating income	24,808	11,200
Other income (expense)	(1,665)	483
Income before income tax provision	23,143	11,683
Income tax provision	4,860	2,542
Equity in net earnings of subsidiaries	0	0
Net income	18,283	9,141
Other comprehensive income, net of tax:
Foreign currency translation adjustments, net of tax expense of $0	10,446	7,370
Total other comprehensive income, net of tax	10,446	7,370
Comprehensive income	$ 28,729	$ 16,511