Note 2 - Marketable Securities - Summary of Unrealized Gains and Losses on Available-for-sale Securities (Details) - USD ($) $ in Thousands	Feb. 25, 2018	Feb. 26, 2017
Amortized cost basis	$ 91,791	$ 136,665
Gross unrealized gains		137
Gross unrealized losses	1,814	650
US Treasury and Government [Member]
Amortized cost basis	80,116	111,727
Gross unrealized gains		136
Gross unrealized losses	1,755	602
Debt Security, Corporate, US [Member]
Amortized cost basis	11,675	24,938
Gross unrealized gains		1
Gross unrealized losses	$ 59	$ 48