Note 4 - Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 26, 2016	Dec. 26, 2015
Fair Value, Inputs, Level 1 [Member] | Cash [Member]
Assets fair value, recurring	$ 75,674	$ 73,746
Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member]
Assets fair value, recurring
Fair Value, Inputs, Level 1 [Member] | Foreign Government Debt Securities [Member]
Assets fair value, recurring
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Assets fair value, recurring
Fair Value, Inputs, Level 1 [Member] | Certificates of Deposit [Member]
Assets fair value, recurring
Fair Value, Inputs, Level 1 [Member]
Assets fair value, recurring	$ 75,674	$ 73,746
Fair Value, Inputs, Level 2 [Member] | Cash [Member]
Assets fair value, recurring
Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Assets fair value, recurring	$ 16,890
Fair Value, Inputs, Level 2 [Member] | Foreign Government Debt Securities [Member]
Assets fair value, recurring	661	$ 650
Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member]
Assets fair value, recurring	21,272	41,624
Fair Value, Inputs, Level 2 [Member] | Certificates of Deposit [Member]
Assets fair value, recurring	24	1,002
Fair Value, Inputs, Level 2 [Member]
Assets fair value, recurring	$ 38,847	$ 43,276
Fair Value, Inputs, Level 3 [Member] | Cash [Member]
Assets fair value, recurring
Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member]
Assets fair value, recurring
Fair Value, Inputs, Level 3 [Member] | Foreign Government Debt Securities [Member]
Assets fair value, recurring
Fair Value, Inputs, Level 3 [Member] | Money Market Funds [Member]
Assets fair value, recurring
Fair Value, Inputs, Level 3 [Member] | Certificates of Deposit [Member]
Assets fair value, recurring
Fair Value, Inputs, Level 3 [Member]
Assets fair value, recurring
Cash [Member]
Assets fair value, recurring	$ 75,674	$ 73,746
Corporate Debt Securities [Member]
Assets fair value, recurring	16,890
Foreign Government Debt Securities [Member]
Assets fair value, recurring	661	650
Money Market Funds [Member]
Assets fair value, recurring	21,272	41,624
Certificates of Deposit [Member]
Assets fair value, recurring	24	1,002
Assets fair value, recurring	$ 114,521	$ 117,022