Quarterly Information - Quarterly Information - Unaudited (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	$ 114,449	$ 103,886	$ 110,550	$ 103,516	$ 92,126	$ 82,861	$ 93,301	$ 63,578	$ 432,401	$ 331,866	$ 238,480
Gross profit	20,752	16,591	18,533	18,853	11,454	15,594	15,849	12,473
Amount released to pre - tax earnings	$ (3,191)	$ (2,202)	$ (1,913)	$ (4,783)	$ (43,062)	$ (27,382)	$ (6,486)	$ (2,890)	$ (12,089)	$ (79,820)	$ 1,373
Net (loss) income per common share attributable to Ampco-Pittsburgh:
Basic	$ (0.26)	$ (0.18)	$ (0.16)	$ (0.39)	$ (3.51)	$ (2.23)	$ (0.53)	$ (0.26)	$ (0.98)	$ (6.68)	$ 0.13
Diluted	$ (0.26)	$ (0.18)	$ (0.16)	$ (0.39)	$ (3.51)	$ (2.23)	$ (0.53)	$ (0.26)	$ (0.98)	$ (6.68)	$ 0.13
Comprehensive (loss) income attributable to Ampco-Pittsburgh	$ 7,320	$ 1,660	$ 2,952	$ (1,808)	$ (47,972)	$ (22,894)	$ (10,739)	$ (1,501)	$ 10,124	$ (83,106)	$ 12,527