Note 3 - Marketable Securities - Summary of Available-for-sale Securities (Details) - USD ($) $ in Thousands	May 31, 2020	Mar. 01, 2020
Available-for-sale securities	$ 112,665	$ 116,945
Fair Value, Inputs, Level 1 [Member]
Available-for-sale securities	112,665	116,945
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	94,120	101,390
US Treasury and Government [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale securities	94,120	101,390
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	18,545	15,555
Debt Security, Corporate, US [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale securities	18,545	15,555
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