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

Reportable Segments - Sales by Geography (Details) - USD ($) $ 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
Revenues from External Customers and Long-Lived Assets
Sales	$ 358,074	$ 391,829	$ 389,267	$ 332,931	$ 322,731	$ 369,979	$ 277,554	$ 93,913	$ 1,472,101	$ 1,064,177	$ 388,875
United States
Revenues from External Customers and Long-Lived Assets
Sales									874,764	705,348	388,875
Netherlands
Revenues from External Customers and Long-Lived Assets
Sales									118,567	79,821	0
United Kingdom
Revenues from External Customers and Long-Lived Assets
Sales									116,410	67,494	0
Other foreign countries
Revenues from External Customers and Long-Lived Assets
Sales									$ 362,360	$ 211,514	$ 0