Note 1 - Description of Business and Summary of Significant Accounting Policies - Reconciliation of Basic to Diluted Weighted-average Shares Outstanding (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Weighted-average shares outstanding – basic (in shares)	73,061	71,848	68,330
Weighted-average shares underlying stock options and restricted shares (in shares)	775	916	657
Weighted-average shares outstanding - diluted (in shares)	73,836	72,764	68,987