Note 6 - Stockholders' Equity (Details Textual) - Common Class A [Member] - USD ($) $ / shares in Units, $ in Billions	1 Months Ended	3 Months Ended			9 Months Ended
	Dec. 31, 2012	Sep. 30, 2015	Sep. 30, 2014	Mar. 31, 2013	Sep. 30, 2015	Sep. 30, 2014	Dec. 11, 2012
Stock Repurchase Program, Authorized Amount							$ 0.1
Stock Repurchased During Period, Shares			264,354
Treasury Stock Acquired, Average Cost Per Share			$ 36.53
Common Stock, Dividends, Per Share, Declared	$ 1		$ 0.25	$ 0.25		$ 0.75