Annual report pursuant to Section 13 and 15(d)

Benefit Plans - Plan Assets (Details)

v3.8.0.1
Benefit Plans - Plan Assets (Details) - Defined Benefit Pension Plans - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Defined Benefit Plan Disclosure      
Fair value of plan assets $ 314,892 $ 285,060  
U.S.      
Defined Benefit Plan Disclosure      
Fair value of plan assets 218,374 198,915 $ 52,678
Quoted Prices in Active Markets (Level 1)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 158,790 147,449  
Significant Other Observable Inputs (Level 2)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 151,952 134,325  
Significant Unobservable Inputs (Level 3)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 4,150 3,286 $ 0
Cash and cash equivalents      
Defined Benefit Plan Disclosure      
Fair value of plan assets 1,072 1,979  
Cash and cash equivalents | Quoted Prices in Active Markets (Level 1)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 934 1,863  
Cash and cash equivalents | Significant Other Observable Inputs (Level 2)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 138 116  
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 50.00%    
Equity Securities | Eco Services Hourly Pension Plan | U.S.      
Defined Benefit Plan Disclosure      
Target asset plan allocation percentage 48.00%    
U.S. investment funds      
Defined Benefit Plan Disclosure      
Fair value of plan assets $ 56,309 60,179  
U.S. investment funds | Quoted Prices in Active Markets (Level 1)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 43,625 41,529  
U.S. investment funds | Significant Other Observable Inputs (Level 2)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 12,684 18,650  
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 70,308 58,457  
International investment funds | Quoted Prices in Active Markets (Level 1)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 28,827 26,119  
International investment funds | Significant Other Observable Inputs (Level 2)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 41,481 32,338  
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 50.00%    
Fixed income securities | Eco Services Hourly Pension Plan | U.S.      
Defined Benefit Plan Disclosure      
Target asset plan allocation percentage 52.00%    
Government securities      
Defined Benefit Plan Disclosure      
Fair value of plan assets $ 11,433 25,437  
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 11,433 25,437  
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 82,585 4,981  
Corporate bonds | Quoted Prices in Active Markets (Level 1)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 77,685 0  
Corporate bonds | Significant Other Observable Inputs (Level 2)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 4,900 4,981  
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 54,263 113,460  
Investment fund bonds | Quoted Prices in Active Markets (Level 1)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 7,719 77,938  
Investment fund bonds | Significant Other Observable Inputs (Level 2)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 46,544 35,522  
Investment fund bonds | Significant Unobservable Inputs (Level 3)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 0 0  
Insurance policies      
Defined Benefit Plan Disclosure      
Fair value of plan assets 38,922 20,567  
Insurance policies | Quoted Prices in Active Markets (Level 1)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 0 0  
Insurance policies | Significant Other Observable Inputs (Level 2)      
Defined Benefit Plan Disclosure      
Fair value of plan assets 34,772 17,281  
Insurance policies | Significant Unobservable Inputs (Level 3)      
Defined Benefit Plan Disclosure      
Fair value of plan assets $ 4,150 $ 3,286