Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements - Financial Assets Valued on Recurring Basis (Details)

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Fair Value Measurements - Financial Assets Valued on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($)
$ in Thousands
Dec. 30, 2017
Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value $ 2,859 $ 6,673
Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value 2,859 6,673
Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value 0 0
Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value 0 0
Market Approach Valuation | Cash and cash equivalents    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value 2,850 6,643
Market Approach Valuation | Short-term investments – mutual funds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value 9 30
Market Approach Valuation | Level 1 | Cash and cash equivalents    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value 2,850 6,643
Market Approach Valuation | Level 1 | Short-term investments – mutual funds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value 9 30
Market Approach Valuation | Level 2 | Cash and cash equivalents    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value 0 0
Market Approach Valuation | Level 2 | Short-term investments – mutual funds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value 0 0
Market Approach Valuation | Level 3 | Cash and cash equivalents    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value 0 0
Market Approach Valuation | Level 3 | Short-term investments – mutual funds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value $ 0 $ 0