Consolidated Balance Sheets (Parentheticals) - USD ($) $ / shares in Thousands, $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Common stock, par value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	71,229,497	70,989,426
Treasury stock, shares (in shares)	5,135,406	4,882,705
Account receivable, allowance for doubtful accounts	$ 3,163	$ 1,794
Common Class A [Member]
Common stock, par value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized (in shares)	15,000,000	15,000,000
Common stock, shares issued (in shares)	8,073,993	7,855,381
Treasury stock, shares (in shares)	1,669,131	1,611,371