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Financial Instruments - Schedule of Carrying and Estimated Fair Value of Other Financial Instruments (Detail) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Reported Value Measurement    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Acquisition-related contingent consideration, including current portion $ 3,750 $ 3,750
Long-term debt 445,000 400,000
Total 448,750 403,750
Level 1 | Estimate of Fair Value Measurement    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Acquisition-related contingent consideration, including current portion 0 0
Long-term debt 0 0
Total 0 0
Level 2 | Estimate of Fair Value Measurement    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Acquisition-related contingent consideration, including current portion 0 0
Long-term debt 452,500 409,000
Total 452,500 409,000
Level 3 | Estimate of Fair Value Measurement    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Acquisition-related contingent consideration, including current portion 3,750 3,750
Long-term debt 0 0
Total $ 3,750 $ 3,750