Note 5 - Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 26, 2015	Dec. 27, 2014
Fair Value, Inputs, Level 1 [Member] | Cash [Member]
Assets fair value, recurring	$ 73,746	$ 66,467
Fair Value, Inputs, Level 1 [Member] | Foreign Government Debt Securities [Member]
Assets fair value, recurring
Fair Value, Inputs, Level 1 [Member] | Municipal 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	$ 73,746	$ 66,467
Fair Value, Inputs, Level 2 [Member] | Cash [Member]
Assets fair value, recurring
Fair Value, Inputs, Level 2 [Member] | Foreign Government Debt Securities [Member]
Assets fair value, recurring	$ 650
Fair Value, Inputs, Level 2 [Member] | Municipal Securities [Member]
Assets fair value, recurring		$ 155
Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member]
Assets fair value, recurring	41,624	4,418
Fair Value, Inputs, Level 2 [Member] | Certificates of Deposit [Member]
Assets fair value, recurring	1,002	1,000
Fair Value, Inputs, Level 2 [Member]
Assets fair value, recurring	$ 43,276	$ 5,573
Fair Value, Inputs, Level 3 [Member] | Cash [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] | Municipal 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	$ 73,746	$ 66,467
Foreign Government Debt Securities [Member]
Assets fair value, recurring	650
Municipal Securities [Member]
Assets fair value, recurring		155
Money Market Funds [Member]
Assets fair value, recurring	41,624	4,418
Certificates of Deposit [Member]
Assets fair value, recurring	1,002	1,000
Assets fair value, recurring	$ 117,022	$ 72,040