Note 7 - Stock-based Compensation - Restricted Stock Activity (Details) - $ / shares					3 Months Ended
	Feb. 08, 2021	Mar. 25, 2020	Apr. 01, 2019	Feb. 25, 2019	Mar. 31, 2021
Restricted Stock [Member]
Outstanding at beginning of year (in shares)					930,854
Outstanding at beginning of year, grant date fair value (in dollars per share)					$ 19.31
Granted (in shares)					52,616
Granted, grant date fair value (in dollars per share)					$ 41.98
Vested (in shares)					(68,365)
Vested, grant date fair value (in dollars per share)					$ 10.07
Forfeited (in shares)					(4,941)
Forfeited, grant date fair value (in dollars per share)					$ 23.94
Outstanding at end of year (in shares)					910,164
Outstanding at end of year, grant date fair value (in dollars per share)					$ 21.29
Market-based Restricted Stock [Member]
Outstanding at beginning of year (in shares)					224,774
Outstanding at beginning of year, grant date fair value (in dollars per share)					$ 19.20
Granted (in shares)	30,616	109,140	29,604	94,247	146,250
Granted, grant date fair value (in dollars per share)					$ 32.14
Vested (in shares)	(231,268)				(231,268)
Vested, grant date fair value (in dollars per share)					$ 26.98
Outstanding at end of year (in shares)					139,756
Outstanding at end of year, grant date fair value (in dollars per share)					$ 21.29