Fair Values of Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Liabilities
Contingent consideration - Current	$ 2,800	$ 2,775
Contingent consideration - Long-term	1,304	2,381
Fair Value Measurements Recurring
Assets
Cash equivalents	2,665	9,569
Assets, fair value	2,815
Liabilities
Liabilities, fair value	4,104	5,156
Fair Value Measurements Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Cash equivalents	2,665	9,569
Assets, fair value	2,665
Fair Value Measurements Recurring | Significant Other Observable Inputs (Level 2)
Assets
Assets, fair value	150
Fair Value Measurements Recurring | Significant Other Unobservable Inputs (Level 3)
Liabilities
Liabilities, fair value	4,104	5,156
Fair Value Measurements Recurring | Prepaid Expenses and Other Current Assets
Assets
Foreign currency forward contracts	150
Fair Value Measurements Recurring | Prepaid Expenses and Other Current Assets | Significant Other Observable Inputs (Level 2)
Assets
Foreign currency forward contracts	150
Fair Value Measurements Recurring | Accrued Expenses and Other Current Liabilities
Liabilities
Contingent consideration - Current	2,800	2,775
Fair Value Measurements Recurring | Accrued Expenses and Other Current Liabilities | Significant Other Unobservable Inputs (Level 3)
Liabilities
Contingent consideration - Current	2,800	2,775
Fair Value Measurements Recurring | Other Liabilities
Liabilities
Contingent consideration - Long-term	1,304	2,381
Fair Value Measurements Recurring | Other Liabilities | Significant Other Unobservable Inputs (Level 3)
Liabilities
Contingent consideration - Long-term	$ 1,304	$ 2,381