| Schedule of Condensed Statements of Income | 
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
|  | Years ended December 31,
 |  
|  | 2020 |  | 2019 |  | 2018 |  
| Stock compensation expense | $ | 25,200 |  |  | $ | 16,212 |  |  | $ | 18,419 |  |  
| Equity in net loss (income) from subsidiaries | 253,571 |  |  | (95,751) |  |  | (76,719) |  |  
| Net (loss) income | (278,771) |  |  | 79,539 |  |  | 58,300 |  |  
| Other comprehensive income (loss), net of tax: |  |  |  |  |  |  
| Pension and postretirement benefits | 1,938 |  |  | 2,430 |  |  | (7,958) |  |  
| Net (loss) gain from hedging activities | 166 |  |  | (2,665) |  |  | (330) |  |  
| Foreign currency translation | (16,596) |  |  | 22,117 |  |  | (35,127) |  |  
| Total other comprehensive income (loss) | (14,492) |  |  | 21,882 |  |  | (43,415) |  |  
| Comprehensive (loss) income | $ | (293,263) |  |  | $ | 101,421 |  |  | $ | 14,885 |  |  
|  |  |  |  |  |  |  | 
| Schedule of Condensed Balance Sheets | 
|  |  |  |  |  |  |  |  |  |  |  |  |  
|  | December 31, 2020
 |  | December 31, 2019
 |  
| ASSETS |  |  |  |  
|  |  |  |  |  
| Investment in subsidiaries | $ | 1,277,126 |  |  | $ | 1,779,450 |  |  
| Total assets | $ | 1,277,126 |  |  | $ | 1,779,450 |  |  
| LIABILITIES |  |  |  |  
|  |  |  |  |  
| Total liabilities | $ | — |  |  | $ | — |  |  
| STOCKHOLDERS' EQUITY |  |  |  |  
| Common stock (0.01 par); authorized shares 450,000,000; issued shares 137,102,143 and 136,861,382 on December 31, 2020 and 2019, respectively; outstanding shares 136,318,557 and 136,464,961 on December 31, 2020 and 2019, respectively | 1,371 |  |  | 1,369 |  |  
| Preferred stock (0.01 par); authorized shares 50,000,000; no shares issued or outstanding on December 31, 2020 and 2019, respectively | — |  |  | — |  |  
| Additional paid-in capital | 1,477,859 |  |  | 1,696,899 |  |  
| (Accumulated deficit) retained earnings | (175,758) |  |  | 103,013 |  |  
| Treasury stock, at cost; shares 783,586 and 396,421 on December 31, 2020 and 2019, respectively | (11,081) |  |  | (6,483) |  |  
| Accumulated other comprehensive loss | (15,265) |  |  | (15,348) |  |  
| Total PQ Group Holdings Inc. equity | 1,277,126 |  |  | 1,779,450 |  |  
| Total liabilities and equity | $ | 1,277,126 |  |  | $ | 1,779,450 |  |  
|  |  |  |  |  | 
| Schedule of Condensed Statements of Cash Flow | 
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
|  | Years ended December 31,
 |  
|  | 2020 |  | 2019 |  | 2018 |  
| Cash flows from operating activities: |  |  |  |  |  |  
| Net (loss) income | $ | (278,771) |  |  | $ | 79,539 |  |  | $ | 58,300 |  |  
| Adjustments to reconcile net (loss) income to net cash provided by operating activities: |  |  |  |  |  |  
| Equity in net income from subsidiaries | 253,571 |  |  | (95,751) |  |  | (76,719) |  |  
| Stock compensation expense | 25,200 |  |  | 16,212 |  |  | 18,419 |  |  
| Net cash provided by operating activities | — |  |  | — |  |  | — |  |  
| Cash flows from investing activities: |  |  |  |  |  |  
| Distribution from subsidiaries | 243,779 |  |  | — |  |  | — |  |  
| Net cash provided by investing activities | 243,779 |  |  | — |  |  | — |  |  
| Cash flows from financing activities: |  |  |  |  |  |  
| Dividends paid to stockholders | (243,779) |  |  | — |  |  | — |  |  
| Net cash used in financing activities | (243,779) |  |  | — |  |  | — |  |  
| Effect of exchange rate changes on cash, cash equivalents and restricted cash | — |  |  | — |  |  | — |  |  
| Net change in cash, cash equivalents and restricted cash | — |  |  | — |  |  | — |  |  
| Cash, cash equivalents and restricted cash at beginning of period | — |  |  | — |  |  | — |  |  
| Cash, cash equivalents and restricted cash at end of period of continuing operations | $ | — |  |  | $ | — |  |  | $ | — |  |  
|  |  |  |  |  |  |  |