Fair Value Measurements - Narrative (Details) $ in Thousands |
Jun. 30, 2018
USD ($)
ft²
|
Dec. 30, 2017
USD ($)
|
|---|---|---|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Restructuring accrual | $ | $ 3,156 | $ 3,494 |
| Massachusetts | ||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Area of real estate property | ft² | 108,743 | |
| Massachusetts | Property Subject to Operating Lease | ||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Area of real estate property | ft² | 25,812 | |
| Restructuring accrual | $ | $ 500 |