Fair Value Measurements - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of other assets	$ 0	$ 67	$ 86	$ 86
Other Payments | Contingent Receivable
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contingent receivable asset	308		308		$ 760
Contingent Receivable | Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain (loss) on contingent receivable	167		299
Payment received on contingent receivable	0		153
Other long-term obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration liability, noncurrent	9,800		9,800		10,700
Accrued expenses
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration liability, current	$ 280		$ 280		289
Other assets (long-term) | Contingent Receivable | Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contingent receivable asset					319
Other current assets | Contingent Receivable | Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contingent receivable asset					$ 441