Supplemental Condensed Consolidating Guarantor and Non-Guarantor Financial Information - Condensed Consolidating Statement Of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net cash provided by operating activities	$ 147,625	$ 233,488	$ 139,920
Investing activities
Payments for acquisition of businesses, net of cash received	(8,929)	(1,251)	(575)
Purchases of property and equipment	(32,004)	(28,935)	(31,399)
Other	295	54	237
Net cash used in investing activities	(40,638)	(30,132)	(31,737)
Financing activities
Payments of long-term debt	0	0	(425,671)
Payments of debt issue costs	0	0	(3,843)
Borrowings under revolving line of credit, net	30,000	(130,000)	200,000
Deposits	2,825	4,006	3,227
Purchase and retirement of common stock	(168,094)	(21,489)	(26,532)
Net issuance of common stock under equity compensation plans	(504)	21,708	16,666
Payments for acquisition-related contingent consideration	(5,161)	(866)	(745)
Other	0	1,331	936
Intercompany transfers	0	0	0
Net cash used in financing activities	(140,934)	(125,310)	(235,962)
Effect of exchange rate changes on cash and cash equivalents	7,750	(11,648)	(6,141)
Net increase (decrease) in cash and cash equivalents	(26,197)	66,398	(133,920)
Cash and cash equivalents, beginning of period	216,158	149,760	283,680
Cash and cash equivalents, end of period	189,961	216,158	149,760
FTI Consulting
Operating activities
Net cash provided by operating activities	25,400	46,908	14,815
Investing activities
Payments for acquisition of businesses, net of cash received	(8,929)	0	0
Purchases of property and equipment	(14,265)	(3,576)	(9,192)
Other	295	54	79
Net cash used in investing activities	(22,899)	(3,522)	(9,113)
Financing activities
Payments of long-term debt			(425,671)
Payments of debt issue costs			(3,843)
Borrowings under revolving line of credit, net	30,000	(130,000)	200,000
Deposits	0	0	0
Purchase and retirement of common stock	(168,094)	(21,489)	(26,532)
Net issuance of common stock under equity compensation plans	(504)	21,708	16,666
Payments for acquisition-related contingent consideration	0	(210)	(451)
Other		1,331	936
Intercompany transfers	98,863	97,483	97,314
Net cash used in financing activities	(39,735)	(31,177)	(141,581)
Effect of exchange rate changes on cash and cash equivalents	0	0	0
Net increase (decrease) in cash and cash equivalents	(37,234)	12,209	(135,879)
Cash and cash equivalents, beginning of period	47,420	35,211	171,090
Cash and cash equivalents, end of period	10,186	47,420	35,211
Guarantor Subsidiaries
Operating activities
Net cash provided by operating activities	80,468	123,101	83,516
Investing activities
Payments for acquisition of businesses, net of cash received	0	0	0
Purchases of property and equipment	(11,893)	(20,185)	(16,487)
Other	0	0	0
Net cash used in investing activities	(11,893)	(20,185)	(16,487)
Financing activities
Payments of long-term debt			0
Payments of debt issue costs			0
Borrowings under revolving line of credit, net	0	0	0
Deposits	0	0	0
Purchase and retirement of common stock	0	0	0
Net issuance of common stock under equity compensation plans	0	0	0
Payments for acquisition-related contingent consideration	(5,161)	(656)	(294)
Other		0	0
Intercompany transfers	(63,411)	(102,269)	(66,729)
Net cash used in financing activities	(68,572)	(102,925)	(67,023)
Effect of exchange rate changes on cash and cash equivalents	0	0	0
Net increase (decrease) in cash and cash equivalents	3	(9)	6
Cash and cash equivalents, beginning of period	156	165	159
Cash and cash equivalents, end of period	159	156	165
Non-Guarantor Subsidiaries
Operating activities
Net cash provided by operating activities	41,757	63,479	41,589
Investing activities
Payments for acquisition of businesses, net of cash received	0	(1,251)	(575)
Purchases of property and equipment	(5,846)	(5,174)	(5,720)
Other	0	0	158
Net cash used in investing activities	(5,846)	(6,425)	(6,137)
Financing activities
Payments of long-term debt			0
Payments of debt issue costs			0
Borrowings under revolving line of credit, net	0	0	0
Deposits	2,825	4,006	3,227
Purchase and retirement of common stock	0	0	0
Net issuance of common stock under equity compensation plans	0	0	0
Payments for acquisition-related contingent consideration	0	0	0
Other		0	0
Intercompany transfers	(35,452)	4,786	(30,585)
Net cash used in financing activities	(32,627)	8,792	(27,358)
Effect of exchange rate changes on cash and cash equivalents	7,750	(11,648)	(6,141)
Net increase (decrease) in cash and cash equivalents	11,034	54,198	1,953
Cash and cash equivalents, beginning of period	168,582	114,384	112,431
Cash and cash equivalents, end of period	$ 179,616	$ 168,582	$ 114,384