Annual report pursuant to Section 13 and 15(d)

Schedule I - Condensed Statements of Operations (Details)

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Schedule I - Condensed Statements of Operations (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Condensed Financial Statements, Captions                      
Stock compensation                 $ 19,464 $ 8,799 $ 5,432
Net income (loss) attributable to PQ Group Holdings Inc. $ 28,119 $ 14,185 $ 15,782 $ 214 $ 65,011 $ (3,345) $ (1,609) $ (2,454) 58,300 57,603 (79,746)
Other comprehensive income (loss), net of tax:                      
Comprehensive income (loss) attributable to PQ Group Holdings Inc.                 14,885 115,625 (134,105)
Parent Company                      
Condensed Financial Statements, Captions                      
Stock compensation                 19,464 8,799 7,029
Equity in net (income) loss from subsidiaries                 (77,764) (66,402) 72,717
Net income (loss) attributable to PQ Group Holdings Inc.                 58,300 57,603 (79,746)
Other comprehensive income (loss), net of tax:                      
Pension and postretirement benefits                 (7,958) (101) 6,865
Net (loss) gain from hedging activities                 (330) (3,590) 4,557
Foreign currency translation                 (35,127) 61,713 (65,781)
Total other comprehensive income (loss)                 (43,415) 58,022 (54,359)
Comprehensive income (loss) attributable to PQ Group Holdings Inc.                 $ 14,885 $ 115,625 $ (134,105)