Quarterly Data (Unaudited) - Schedule of Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 73,543	$ 84,987	$ 93,870	$ 92,651	$ 99,982	$ 101,596	$ 112,258	$ 103,175	$ 345,051	$ 417,011	$ 367,422
Gross profit	25,646	27,133	28,486	31,929	35,667	33,676	33,930	31,586	113,194	134,859	109,171
Net income (loss)	(11,589)	3,036	5,486	38	(51,172)	5,826	4,037	3,055	$ (3,029)	$ (38,218)	$ (5,602)
Net income (loss) attributable to CECO Environmental Corp.	$ (11,589)	$ 3,036	$ 5,486	$ 38	$ (51,172)	$ 5,804	$ 4,050	$ 3,100
Basic earnings (loss) per share	$ (0.34)	$ 0.09	$ 0.16	$ 0.00	$ (1.49)	$ 0.17	$ 0.12	$ 0.09	$ (0.09)	$ (1.12)	$ (0.19)
Diluted earnings (loss) per share	$ (0.34)	$ 0.09	$ 0.16	$ 0.00	$ (1.49)	$ 0.17	$ 0.12	$ 0.09	$ (0.09)	$ (1.12)	$ (0.19)