Earnings per Share (Tables)
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6 Months Ended | 
Jun. 30, 2019  | 
| Earnings Per Share [Abstract] | 
 
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| Reconciliation from Basic to Diluted Weighted Average Number of Shares Outstanding | 
 The reconciliation from basic to diluted weighted average shares outstanding is as follows:  
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Three months ended June 30,  | 
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Six months ended June 30,  | 
 
   | 
   | 
2019  | 
   | 
2018  | 
   | 
2019  | 
   | 
2018  | 
 
Weighted average shares outstanding – Basic  | 
   | 
134,142,552  | 
 
  | 
   | 
133,222,463  | 
 
  | 
   | 
134,044,972  | 
 
  | 
   | 
133,188,303  | 
 
  | 
 
Dilutive effect of unvested common shares and restricted stock units with service conditions, performance stock units considered probable of vesting and assumed stock option exercises and conversions  | 
   | 
1,180,472  | 
 
  | 
   | 
987,277  | 
 
  | 
   | 
1,062,035  | 
 
  | 
   | 
859,059  | 
 
  | 
 
Weighted average shares outstanding – Diluted  | 
   | 
135,323,024  | 
 
  | 
   | 
134,209,740  | 
 
  | 
   | 
135,107,007  | 
 
  | 
   | 
134,047,362  | 
 
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| Schedule of Earnings Per Share, Basic and Diluted | 
 Basic and diluted earnings per share are calculated as follows: 
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   | 
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Three months ended June 30,  | 
   | 
Six months ended June 30,  | 
 
   | 
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2019  | 
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2018  | 
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2019  | 
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2018  | 
 
Numerator:  | 
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Net income attributable to PQ Group Holdings Inc.  | 
   | 
$  | 
30,574  | 
 
  | 
   | 
$  | 
15,782  | 
 
  | 
   | 
$  | 
33,725  | 
 
  | 
   | 
$  | 
15,996  | 
 
  | 
 
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Denominator:  | 
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Weighted average shares outstanding – Basic  | 
   | 
134,142,552  | 
 
  | 
   | 
133,222,463  | 
 
  | 
   | 
134,044,972  | 
 
  | 
   | 
133,188,303  | 
 
  | 
 
Weighted average shares outstanding – Diluted  | 
   | 
135,323,024  | 
 
  | 
   | 
134,209,740  | 
 
  | 
   | 
135,107,007  | 
 
  | 
   | 
134,047,362  | 
 
  | 
 
Net income per share:  | 
   | 
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Basic income per share  | 
   | 
$  | 
0.23  | 
 
  | 
   | 
$  | 
0.12  | 
 
  | 
   | 
$  | 
0.25  | 
 
  | 
   | 
$  | 
0.12  | 
 
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Diluted income per share  | 
   | 
$  | 
0.23  | 
 
  | 
   | 
$  | 
0.12  | 
 
  | 
   | 
$  | 
0.25  | 
 
  | 
   | 
$  | 
0.12  | 
 
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| Schedule of Securities Excluded from Computation of Earnings Per Share | 
 The table below presents the details of the Company’s weighted average equity-based awards outstanding during each respective period that were excluded from the calculation of diluted earnings per share: 
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   | 
   | 
Three months ended June 30,  | 
   | 
Six months ended June 30,  | 
 
   | 
   | 
2019  | 
 
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2018  | 
   | 
2019  | 
 
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2018  | 
 
Restricted stock awards with performance only targets not yet achieved  | 
   | 
1,637,134  | 
 
  | 
   | 
1,760,937  | 
 
  | 
   | 
1,638,318  | 
 
  | 
   | 
1,760,937  | 
 
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Stock options with performance only targets not yet achieved  | 
   | 
586,253  | 
 
  | 
   | 
586,253  | 
 
  | 
   | 
586,253  | 
 
  | 
   | 
586,253  | 
 
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Anti-dilutive restricted stock awards, restricted stock units and performance stock units  | 
   | 
—  | 
 
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   | 
—  | 
 
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   | 
2,102  | 
 
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   | 
—  | 
 
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Anti-dilutive stock options  | 
   | 
863,063  | 
 
  | 
   | 
621,747  | 
 
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   | 
863,063  | 
 
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   | 
621,747  | 
 
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