Annual report pursuant to Section 13 and 15(d)

Benefit Plans - Plan Assets (Details)

v3.10.0.1
Benefit Plans - Plan Assets (Details) - Defined Benefit Pension Plans - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Defined Benefit Plan Disclosure      
Fair value of plan assets $ 287,542 $ 314,892  
U.S.      
Defined Benefit Plan Disclosure      
Fair value of plan assets 195,755 218,374 $ 198,915
Quoted Prices in Active Markets (Level 1)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 195,949 158,790  
Significant Other Observable Inputs (Level 2)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 86,572 151,952  
Significant Unobservable Inputs (Level 3)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 5,021 4,150 $ 3,286
Cash and cash equivalents      
Defined Benefit Plan Disclosure      
Fair value of plan assets 57,000 1,072  
Cash and cash equivalents | U.S.      
Defined Benefit Plan Disclosure      
Fair value of plan assets 56    
Cash and cash equivalents | Quoted Prices in Active Markets (Level 1)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 56,925 934  
Cash and cash equivalents | Significant Other Observable Inputs (Level 2)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 75 138  
Cash and cash equivalents | Significant Unobservable Inputs (Level 3)      
Defined Benefit Plan Disclosure      
Fair value of plan assets $ 0 0  
Equity Securities | PQ Corporation Retirement Plan | U.S.      
Defined Benefit Plan Disclosure      
Target asset plan allocation percentage 45.00%    
Equity Securities | Eco Services Pension Equity Plan | U.S.      
Defined Benefit Plan Disclosure      
Target asset plan allocation percentage 40.00%    
Equity Securities | Eco Services Hourly Pension Plan | U.S.      
Defined Benefit Plan Disclosure      
Target asset plan allocation percentage 45.00%    
U.S. investment funds      
Defined Benefit Plan Disclosure      
Fair value of plan assets $ 35,103 56,309  
U.S. investment funds | Quoted Prices in Active Markets (Level 1)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 35,103 43,625  
U.S. investment funds | Significant Other Observable Inputs (Level 2)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 0 12,684  
U.S. investment funds | Significant Unobservable Inputs (Level 3)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 0 0  
International investment funds      
Defined Benefit Plan Disclosure      
Fair value of plan assets 44,508 70,308  
International investment funds | Quoted Prices in Active Markets (Level 1)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 24,040 28,827  
International investment funds | Significant Other Observable Inputs (Level 2)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 20,468 41,481  
International investment funds | Significant Unobservable Inputs (Level 3)      
Defined Benefit Plan Disclosure      
Fair value of plan assets $ 0 0  
Fixed income securities | PQ Corporation Retirement Plan | U.S.      
Defined Benefit Plan Disclosure      
Target asset plan allocation percentage 55.00%    
Fixed income securities | Eco Services Pension Equity Plan | U.S.      
Defined Benefit Plan Disclosure      
Target asset plan allocation percentage 60.00%    
Fixed income securities | Eco Services Hourly Pension Plan | U.S.      
Defined Benefit Plan Disclosure      
Target asset plan allocation percentage 55.00%    
Government securities      
Defined Benefit Plan Disclosure      
Fair value of plan assets $ 10,121 11,433  
Government securities | Quoted Prices in Active Markets (Level 1)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 0 0  
Government securities | Significant Other Observable Inputs (Level 2)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 10,121 11,433  
Government securities | Significant Unobservable Inputs (Level 3)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 0 0  
Corporate bonds      
Defined Benefit Plan Disclosure      
Fair value of plan assets 77,229 82,585  
Corporate bonds | Quoted Prices in Active Markets (Level 1)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 72,216 77,685  
Corporate bonds | Significant Other Observable Inputs (Level 2)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 5,013 4,900  
Corporate bonds | Significant Unobservable Inputs (Level 3)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 0 0  
Investment fund bonds      
Defined Benefit Plan Disclosure      
Fair value of plan assets 25,152 54,263  
Investment fund bonds | Quoted Prices in Active Markets (Level 1)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 7,665 7,719  
Investment fund bonds | Significant Other Observable Inputs (Level 2)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 17,487 46,544  
Investment fund bonds | Significant Unobservable Inputs (Level 3)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 0 0  
Insurance contracts      
Defined Benefit Plan Disclosure      
Fair value of plan assets 38,429 38,922  
Insurance contracts | Quoted Prices in Active Markets (Level 1)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 0 0  
Insurance contracts | Significant Other Observable Inputs (Level 2)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 33,408 34,772  
Insurance contracts | Significant Unobservable Inputs (Level 3)      
Defined Benefit Plan Disclosure      
Fair value of plan assets $ 5,021 $ 4,150