Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net (loss) income	$ (11,302)	$ (79,809)	$ 1,373
Adjustments for changes in:
Foreign exchange translation	11,041	(14,580)	(3,967)
Unrecognized employee benefit costs (including effects of foreign currency translation)	7,299	9,397	10,713
Unrealized holding gains (losses) on marketable securities	602	405	(239)
Fair value of cash flow hedges	804	398	(475)
Reclassification adjustments for items included in net (loss) income:
Amortization of unrecognized employee benefit costs	3,283	1,910	4,740
Realized gains from sale of marketable securities	(29)	(1,038)	(53)
Realized (gains) losses from settlement of cash flow hedges	(670)	108	435
Other comprehensive income (loss)	22,330	(3,400)	11,154
Comprehensive income (loss)	11,028	(83,209)	12,527
Less: Comprehensive income (loss) attributable to noncontrolling interest	904	(103)	0
Comprehensive income (loss) income attributable to Ampco-Pittsburgh	$ 10,124	$ (83,106)	$ 12,527