Note 3 - Marketable Securities - Summary of Unrealized Gains and Losses on Available-for-sale Securities (Details) - USD ($) $ in Thousands	Nov. 25, 2018	Feb. 25, 2018
Amortized cost basis	$ 97,047	$ 91,791
Gross unrealized gains	1
Gross unrealized losses	1,657	1,814
US Treasury and Government [Member]
Amortized cost basis	76,070	80,116
Gross unrealized gains
Gross unrealized losses	1,607	1,755
Debt Security, Corporate, US [Member]
Amortized cost basis	20,977	11,675
Gross unrealized gains	1
Gross unrealized losses	$ 50	$ 59