Financial Instruments (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Expense related to increase in fair value of future expected contingent consideration	$ 0	$ 0
Reported Value Measurement
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Acquisition-related contingent consideration, including current portion	2,960,000		$ 2,960,000
Long-term debt	316,250,000		316,250,000
Total	319,210,000		319,210,000
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	317,783,000		291,837,000
Total	317,783,000		291,837,000
Level 3 | Estimate of Fair Value Measurement
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Acquisition-related contingent consideration, including current portion	2,960,000		2,960,000
Long-term debt	0		0
Total	$ 2,960,000		$ 2,960,000