Note 10 - Stockholders' Equity - Dividend Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Per share amount (in dollars per share)	$ 0.38	$ 0.34	$ 0.28
Quarterly Dividends 1 [Member]
Record date	Mar. 19, 2020	Apr. 05, 2019
Per share amount (in dollars per share)	$ 1,917	$ 1,672
Quarterly Dividends 2 [Member]
Record date	Jun. 04, 2020	Jun. 06, 2019
Per share amount (in dollars per share)	$ 1,917	$ 1,672
Quarterly Dividends 3 [Member]
Record date	Sep. 10, 2020	Sep. 05, 2019
Per share amount (in dollars per share)	$ 1,925	$ 1,691
Quarterly Dividends 4 [Member]
Record date	Dec. 03, 2020	Dec. 05, 2019
Per share amount (in dollars per share)	$ 1,936	$ 1,701