v3.19.3
Debt - Additional Information (Detail)
3 Months Ended 9 Months Ended
Dec. 31, 2018
USD ($)
Dec. 06, 2017
Feb. 21, 2017
Aug. 18, 2016
USD ($)
Dec. 31, 2018
USD ($)
Sep. 30, 2019
USD ($)
covenant
Sep. 30, 2018
USD ($)
Amended and Restated Credit Agreement              
Debt Instrument [Line Items]              
Number of covenants | covenant           1  
Debt covenant trigger, line of credit facility amount less letters of credit threshold           $ 22,500,000  
Amended and Restated Credit Agreement | Maximum              
Debt Instrument [Line Items]              
Leverage ratio (no greater than)           5.0  
Term Loan Facility | Amended and Restated Credit Agreement              
Debt Instrument [Line Items]              
Debt principal amount       $ 275,000,000      
Decrease in basis spread, percentage     0.25%        
Leverage ratio (no greater than)   1.1     1.1    
Schedule principal payments           $ 2,000,000.0 $ 2,000,000.0
Effective interest rate           4.50%  
Term Loan Facility | Amended and Restated Credit Agreement | London Interbank Offered Rate (LIBOR)              
Debt Instrument [Line Items]              
Debt, variable interest rate 2.00% 2.25% 2.50% 2.75%   2.00%  
Floor rate       0.75%   0.75%  
Debt, variable interest rate if leverage ratio met   2.00%          
Line of Credit | Amended and Restated Credit Agreement | Revolving Credit Facility              
Debt Instrument [Line Items]              
Line of credit facility borrowing capacity       $ 75,000,000.0      
Debt, variable interest rate           2.25%  
Outstanding amount $ 0       $ 0 $ 0  
Facility fee, basis points           0.50%  
Remaining outstanding           $ 73,700,000  
Line of Credit | Industrial revenue bonds | Industrial Revenue Bonds              
Debt Instrument [Line Items]              
Line of credit facility borrowing capacity $ 28,000,000.0       $ 28,000,000.0    
Line of Credit | Industrial revenue bonds | Industrial Revenue Bonds | London Interbank Offered Rate (LIBOR)              
Debt Instrument [Line Items]              
Debt, variable interest rate           1.50%  
Reduction in rate related to the tax-free interest income           20.00%