Note 8 - Stockholders' Equity (Details Textual)	12 Months Ended			53 Months Ended
	Dec. 31, 2015 shares	Dec. 31, 2014 shares	Dec. 31, 2013 shares	Dec. 31, 2015 $ / shares shares	Jul. 20, 2012 shares	Aug. 31, 2011 shares
Common Class A [Member] | Additional Shares Authorized [Member]
Stock Repurchase Program, Number of Shares Authorized to be Repurchased					1,000,000
Common Class A [Member]
Conversion of Common Stock Shares	1
Common Stock Number of Votes	1
Stock Repurchase Program, Number of Shares Authorized to be Repurchased						2,000,000
Stock Repurchased During Period, Shares	228,737	226,729	127,900	1,700,000
Treasury Stock Acquired, Average Cost Per Share | $ / shares				$ 41.34
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased	1,300,000			1,300,000
Common Class B [Member]
Percentage of Class B Common to Total Common Stock Subject to Automatic Conversion	1.00%
Common Stock Number of Votes	10