Ecovyst, Inc. Annual report pursuant to Section 13 and 15(d)

Financial Instruments - Cash Flow Hedge Impact on Statement of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Cost of goods sold	$ (1,226,520)	$ (1,095,265)	$ (810,085)
Interest (expense) income	(113,723)	(179,044)	(140,315)
Gain (loss) on cash flow hedging relationships: \| Amount of gain (loss) reclassified from AOCI into income \| Interest rate caps
Derivative [Line Items]
Cost of goods sold	0	0	0
Interest (expense) income	(256)	(40)	0
Gain (loss) on cash flow hedging relationships: \| Amount of gain (loss) reclassified from AOCI into income \| Natural gas swaps
Derivative [Line Items]
Cost of goods sold	353	(222)	(1,433)
Interest (expense) income	$ 0	$ 0	$ 0