Note 2 - Marketable Securities - Summary of Available-for-sale Securities (Details) - USD ($) $ in Thousands	Feb. 25, 2018	Feb. 26, 2017
Available-for-sale securities	$ 89,977	$ 136,152
Fair Value, Inputs, Level 1 [Member]
Available-for-sale securities	89,977	136,152
Fair Value, Inputs, Level 2 [Member]
Available-for-sale securities
Fair Value, Inputs, Level 3 [Member]
Available-for-sale securities
US Treasury and Government [Member]
Available-for-sale securities	78,361	111,261
US Treasury and Government [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale securities	78,361	111,261
US Treasury and Government [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale securities
US Treasury and Government [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale securities
Debt Security, Corporate, US [Member]
Available-for-sale securities	11,616	24,891
Debt Security, Corporate, US [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale securities	11,616	24,891
Debt Security, Corporate, US [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale securities
Debt Security, Corporate, US [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale securities