Fair Value Measurements (Details) - USD ($) $ in Thousands | 6 Months Ended | 12 Months Ended |
Jun. 30, 2018 | Dec. 31, 2017 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Document Period End Date | Jun. 30, 2018 | |
Asset impairment charges | | $ 8,800 |
Fair Value, Measurements, Recurring | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash Equivalents | $ 6,811 | 12,942 |
Available for Sale Securities | 59,987 | 57,303 |
Interest rate swap contract | 561 | 762 |
Assets measured at fair value | 67,359 | 71,007 |
Total liabilities measured at fair value | (667) | |
Fair Value, Measurements, Recurring | Level 1 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash Equivalents | 1,821 | 10,946 |
Available for Sale Securities | 0 | 0 |
Interest rate swap contract | 0 | 0 |
Assets measured at fair value | 1,821 | 10,946 |
Total liabilities measured at fair value | 0 | |
Fair Value, Measurements, Recurring | Level 2 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash Equivalents | 4,990 | 1,996 |
Available for Sale Securities | 59,987 | 57,303 |
Interest rate swap contract | 561 | 762 |
Assets measured at fair value | 65,538 | 60,061 |
Total liabilities measured at fair value | (667) | |
Fair Value, Measurements, Recurring | Level 3 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash Equivalents | 0 | 0 |
Available for Sale Securities | 0 | 0 |
Interest rate swap contract | 0 | 0 |
Assets measured at fair value | 0 | 0 |
Total liabilities measured at fair value | 0 | |
Fair Value, Measurements, Recurring | Money market funds | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash Equivalents | 1,821 | 10,946 |
Fair Value, Measurements, Recurring | Money market funds | Level 1 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash Equivalents | 1,821 | 10,946 |
Fair Value, Measurements, Recurring | Money market funds | Level 2 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash Equivalents | 0 | 0 |
Fair Value, Measurements, Recurring | Money market funds | Level 3 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash Equivalents | 0 | 0 |
Fair Value, Measurements, Recurring | Commercial paper | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash Equivalents | 4,990 | 1,996 |
Fair Value, Measurements, Recurring | Commercial paper | Level 1 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash Equivalents | 0 | 0 |
Fair Value, Measurements, Recurring | Commercial paper | Level 2 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash Equivalents | 4,990 | 1,996 |
Fair Value, Measurements, Recurring | Commercial paper | Level 3 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash Equivalents | 0 | 0 |
Fair Value, Measurements, Recurring | Certificates of deposit | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for Sale Securities | 20,380 | 19,875 |
Fair Value, Measurements, Recurring | Certificates of deposit | Level 1 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for Sale Securities | 0 | 0 |
Fair Value, Measurements, Recurring | Certificates of deposit | Level 2 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for Sale Securities | 20,380 | 19,875 |
Fair Value, Measurements, Recurring | Certificates of deposit | Level 3 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for Sale Securities | 0 | 0 |
Fair Value, Measurements, Recurring | Corporate bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for Sale Securities | 24,631 | 29,239 |
Fair Value, Measurements, Recurring | Corporate bonds | Level 1 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for Sale Securities | 0 | 0 |
Fair Value, Measurements, Recurring | Corporate bonds | Level 2 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for Sale Securities | 24,631 | 29,239 |
Fair Value, Measurements, Recurring | Corporate bonds | Level 3 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for Sale Securities | 0 | 0 |
Fair Value, Measurements, Recurring | U.S. government bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for Sale Securities | 14,976 | 8,189 |
Fair Value, Measurements, Recurring | U.S. government bonds | Level 1 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for Sale Securities | 0 | 0 |
Fair Value, Measurements, Recurring | U.S. government bonds | Level 2 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for Sale Securities | 14,976 | 8,189 |
Fair Value, Measurements, Recurring | U.S. government bonds | Level 3 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for Sale Securities | 0 | 0 |
Interest rate swap contract | Fair Value, Measurements, Recurring | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Interest rate swap contract | 561 | 372 |
Interest rate swap contract | Fair Value, Measurements, Recurring | Level 1 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Interest rate swap contract | 0 | 0 |
Interest rate swap contract | Fair Value, Measurements, Recurring | Level 2 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Interest rate swap contract | 561 | 372 |
Interest rate swap contract | Fair Value, Measurements, Recurring | Level 3 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Interest rate swap contract | 0 | 0 |
Foreign currency forward contracts | Fair Value, Measurements, Recurring | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Interest rate swap contract | | 390 |
Foreign currency forward contracts | Fair Value, Measurements, Recurring | Level 1 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Interest rate swap contract | | 0 |
Foreign currency forward contracts | Fair Value, Measurements, Recurring | Level 2 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Interest rate swap contract | | 390 |
Foreign currency forward contracts | Fair Value, Measurements, Recurring | Level 3 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Interest rate swap contract | | $ 0 |
Foreign currency forward contracts | Fair Value, Measurements, Recurring | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Foreign currency forward contracts | (667) | |
Foreign currency forward contracts | Fair Value, Measurements, Recurring | Level 1 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Foreign currency forward contracts | 0 | |
Foreign currency forward contracts | Fair Value, Measurements, Recurring | Level 2 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Foreign currency forward contracts | (667) | |
Foreign currency forward contracts | Fair Value, Measurements, Recurring | Level 3 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Foreign currency forward contracts | $ 0 | |