Financial Instruments - Schedule of Carrying and Estimated Fair Value of Other Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Reported Value Measurement
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Acquisition-related contingent consideration, including current portion	$ 2,960	$ 3,750
Long-term debt	375,000	400,000
Total	377,960	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	381,750	409,000
Total	381,750	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	2,960	3,750
Long-term debt	0	0
Total	$ 2,960	$ 3,750