Organization and Significant Accounting Policies (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014 segment unit	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues from external customers	$ 79,017us-gaap_Revenues	$ 109,338us-gaap_Revenues	$ 97,644us-gaap_Revenues
Treasury Stock, Shares, Acquired	58,649us-gaap_TreasuryStockSharesAcquired	99,531us-gaap_TreasuryStockSharesAcquired
Revenues	79,017us-gaap_Revenues	109,338us-gaap_Revenues	97,644us-gaap_Revenues
Percentage Of Net Income, Foreign	36.00%ftek_PercentageOfNetIncomeForeign	42.00%ftek_PercentageOfNetIncomeForeign	28.00%ftek_PercentageOfNetIncomeForeign
Restricted Cash and Cash Equivalents	1,639
Unbilled Contracts Receivable	6,910us-gaap_UnbilledContractsReceivable	10,693us-gaap_UnbilledContractsReceivable
Number of Reportable Segments	2us-gaap_NumberOfReportableSegments
Number of Reporting Units	2ftek_NumberofReportingUnits
Finite-Lived Patents, Gross	1,583us-gaap_FiniteLivedPatentsGross	1,273us-gaap_FiniteLivedPatentsGross
Identifiable intangible assets	5,158
Payments to Acquire Intangible Assets	3,010	0	0
Useful Life (Yrs)	5 years
Amortization of Intangible Assets	2,384us-gaap_AmortizationOfIntangibleAssets	839us-gaap_AmortizationOfIntangibleAssets	898us-gaap_AmortizationOfIntangibleAssets
Depreciation	1,922us-gaap_Depreciation	2,175us-gaap_Depreciation	2,191us-gaap_Depreciation
Stock Awards Available for Issuance Under the Incentive Plan (in shares)	1,960,000
Options, Outstanding, Number (in shares)	1,546,500	1,688,500	1,914,000	1,902,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	280,000
Available-for-sale Securities, Fair Value Disclosure	36us-gaap_AvailableForSaleSecurities	30us-gaap_AvailableForSaleSecurities
Treasury Stock, Value, Acquired, Cost Method	304	447	39
Sales Revenue, Services, Net
Concentration Risk, Percentage	10.00%	10.00%	10.00%
Number of Customers	2	2	1
Accounts Receivable
Concentration Risk, Percentage	10.00%	10.00%	10.00%
Number of Customers	0	0	0
Capitalized Third-party Costs
Finite-Lived Patents, Gross	376	305
Minimum
Standard Product Warranty Description (in years)	1 year
Maximum
Standard Product Warranty Description (in years)	2 years
Antidilutive
Options, Outstanding, Number (in shares)	1,628,000	1,623,000	1,507,000
FUEL CHEM Segment
Revenues from external customers	36,986	36,786	35,203
Revenues	36,986	36,786	35,203
FUEL CHEM Segment \| Sales Revenue, Services, Net
Concentration Risk, Percentage	20.00%
Number of Customers	1
APC Technology Segment \| Sales Revenue, Services, Net
Concentration Risk, Percentage	11.00%
Customer One \| FUEL CHEM Segment \| Sales Revenue, Services, Net
Concentration Risk, Percentage		14.00%	16.00%
Customer One \| APC Technology Segment \| Sales Revenue, Services, Net
Concentration Risk, Percentage		18.00%
Project and Non-Project
Unbilled Contracts Receivable	9,904	12,599
Foreign
Revenues from external customers	28,116	46,063	27,219
Revenues	$ 28,116	$ 46,063	$ 27,219
Reserved For Issuance Upon Exercise Or Vesting Of Equity Awards
Common Stock, Capital Shares Reserved for Future Issuance	4,483,525	2,460,516

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