Condensed Consolidated Statements of Shareholders' Equity (Unaudited) (Parentheticals) - $ / shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Common Stock [Member]
Shares of stock (in shares)	28,657
Shares of common stock for the exercise of stock options (in shares)	86,247
Shares of restricted common shares, net of (forfeitures) (in shares)	6,005
Dividends declared per common share (in dollars per share)	$ 0.19
Common Class A [Member]
Shares of stock (in shares)		30,180
Shares of common stock for the exercise of stock options (in shares)		74,769
Shares of restricted common shares, net of (forfeitures) (in shares)		6,793
Dividends declared per common share (in dollars per share)		$ 0.10
Common Class B [Member]
Shares of stock (in shares)		3,677
Shares of common stock for the exercise of stock options (in shares)		9,296
Dividends declared per common share (in dollars per share)		$ 0.60
Shares of common stock for the exercise of stock options (in shares)	86,247
Dividends declared per common share (in dollars per share)	$ 0.19