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Acquisitions - Additional Information (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
May 20, 2019
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Dec. 31, 2018
Business Acquisition [Line Items]            
Payments to acquire businesses       $ 33,196 $ 0  
Goodwill   $ 433,156   433,156   $ 413,640
Estimated future amortization expense, remainder of fiscal year   600   600    
Revenues   349,675 $ 339,331 675,713 665,225  
Net income   39,806 $ 33,179 63,038 $ 65,550  
Sierra Monitor Corporation            
Business Acquisition [Line Items]            
Voting interest acquired (percentage) 100.00%          
Payments to acquire businesses $ 33,200          
Goodwill 19,800 $ 19,800   19,800    
Estimated future amortization expense, year 1 1,200          
Estimated future amortization expense, year 2 1,200          
Estimated future amortization expense, year 3 1,200          
Estimated future amortization expense, year 4 1,200          
Estimated future amortization expense, year 5 1,200          
Estimated future amortization expense, thereafter 5,300          
Step up to fair value of acquired inventory $ 1,600          
Period of amortization of step up to fair value of acquired inventory 6 months          
Transaction costs       2,000    
Revenues       2,600    
Net income       $ (1,500)    
Customer relationships | Sierra Monitor Corporation            
Business Acquisition [Line Items]            
Useful life 10 years          
Technology | Sierra Monitor Corporation            
Business Acquisition [Line Items]            
Useful life 5 years          
Stock Options And Restricted Stock Units | Sierra Monitor Corporation            
Business Acquisition [Line Items]            
Goodwill $ 900