Supplemental Condensed Consolidating Guarantor and Non-Guarantor Financial Information - Condensed Consolidating Balance Sheet Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 152,044	$ 189,961	$ 120,959	$ 216,158
Accounts receivable, net	583,588	522,878
Intercompany receivables	0	0
Other current assets	80,146	81,340
Total current assets	815,778	794,179
Property and equipment, net	75,586	75,075
Goodwill	1,208,011	1,204,803
Other intangible assets, net	42,390	44,150
Investments in subsidiaries	0	0
Other assets	134,687	139,034
Total assets	2,276,452	2,257,241
Liabilities
Intercompany payables	0	0
Other current liabilities	343,467	410,328
Total current liabilities	343,467	410,328
Long-term debt, net	441,473	396,284
Other liabilities	254,078	258,658
Total liabilities	1,039,018	1,065,270
Stockholders' equity	1,237,434	1,191,971
Total liabilities and stockholders' equity	2,276,452	2,257,241
Eliminations
Assets
Cash and cash equivalents	0	0
Accounts receivable, net	0	0
Intercompany receivables	(1,119,886)	(1,125,906)
Other current assets	0	0
Total current assets	(1,119,886)	(1,125,906)
Property and equipment, net	0	0
Goodwill	0	0
Other intangible assets, net	(14,160)	(14,968)
Investments in subsidiaries	(2,769,577)	(2,742,273)
Other assets	0	0
Total assets	(3,903,623)	(3,883,147)
Liabilities
Intercompany payables	(1,119,886)	(1,125,906)
Other current liabilities	0	0
Total current liabilities	(1,119,886)	(1,125,906)
Long-term debt, net	0	0
Other liabilities	0	0
Total liabilities	(1,119,886)	(1,125,906)
Stockholders' equity	(2,783,737)	(2,757,241)
Total liabilities and stockholders' equity	(3,903,623)	(3,883,147)
FTI Consulting
Assets
Cash and cash equivalents	8,406	10,186	18,371	47,420
Accounts receivable, net	185,359	155,124
Intercompany receivables	0	0
Other current assets	28,620	31,933
Total current assets	222,385	197,243
Property and equipment, net	39,967	39,137
Goodwill	570,876	570,876
Other intangible assets, net	17,552	18,426
Investments in subsidiaries	2,224,753	2,175,362
Other assets	32,297	34,454
Total assets	3,107,830	3,035,498
Liabilities
Intercompany payables	1,119,886	1,125,906
Other current liabilities	110,376	127,295
Total current liabilities	1,230,262	1,253,201
Long-term debt, net	441,473	396,284
Other liabilities	198,661	194,042
Total liabilities	1,870,396	1,843,527
Stockholders' equity	1,237,434	1,191,971
Total liabilities and stockholders' equity	3,107,830	3,035,498
Guarantor Subsidiaries
Assets
Cash and cash equivalents	157	159	157	156
Accounts receivable, net	181,692	156,859
Intercompany receivables	1,114,635	1,093,211
Other current assets	23,096	21,840
Total current assets	1,319,580	1,272,069
Property and equipment, net	12,508	13,572
Goodwill	416,053	416,053
Other intangible assets, net	10,838	11,251
Investments in subsidiaries	544,824	566,911
Other assets	65,651	60,566
Total assets	2,369,454	2,340,422
Liabilities
Intercompany payables	0	0
Other current liabilities	128,921	144,474
Total current liabilities	128,921	144,474
Long-term debt, net	0	0
Other liabilities	10,308	14,753
Total liabilities	139,229	159,227
Stockholders' equity	2,230,225	2,181,195
Total liabilities and stockholders' equity	2,369,454	2,340,422
Non-Guarantor Subsidiaries
Assets
Cash and cash equivalents	143,481	179,616	$ 102,431	$ 168,582
Accounts receivable, net	216,537	210,895
Intercompany receivables	5,251	32,695
Other current assets	28,430	27,567
Total current assets	393,699	450,773
Property and equipment, net	23,111	22,366
Goodwill	221,082	217,874
Other intangible assets, net	28,160	29,441
Investments in subsidiaries	0	0
Other assets	36,739	44,014
Total assets	702,791	764,468
Liabilities
Intercompany payables	0	0
Other current liabilities	104,170	138,559
Total current liabilities	104,170	138,559
Long-term debt, net	0	0
Other liabilities	45,109	49,863
Total liabilities	149,279	188,422
Stockholders' equity	553,512	576,046
Total liabilities and stockholders' equity	$ 702,791	$ 764,468