Note 5 - Share-Based Compensation (Details) - Stock Option Activity (USD $)	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Common Class A [Member]
Note 5 - Share-Based Compensation (Details) - Stock Option Activity [Line Items]
Number of options outstanding	1,367,754
Weighted average exercise price of options outstanding (in Dollars per share)	$ 8.45
Number of options granted	232,344	238,890
Weighted average exercise price of options granted (in Dollars per share)	$ 15.98
Number of options exercised	(119,253)
Weighted average exercise price of options exercised (in Dollars per share)	$ 2.20
Number of options outstanding	1,480,845
Weighted average exercise price of options outstanding (in Dollars per share)	$ 10.14
Weighted average remaining contractual term of options outstanding	6 years 240 days
Aggregate intrinsic value of options outstanding (in Dollars)	$ 12,872
Number of options exercisable	729,975
Weighted average exercise price of options exercisable (in Dollars per share)	$ 8.87
Weighted average remaining contractual term of options exercisable	5 years 193 days
Aggregate intrinsic value of options exercisable (in Dollars)	7,271
Common Class B [Member]
Note 5 - Share-Based Compensation (Details) - Stock Option Activity [Line Items]
Number of options outstanding	227,959
Weighted average exercise price of options outstanding (in Dollars per share)	$ 18.45
Number of options granted	38,718	39,815
Weighted average exercise price of options granted (in Dollars per share)	$ 29.35
Number of options exercised	(19,875)
Weighted average exercise price of options exercised (in Dollars per share)	$ 13.20
Number of options outstanding	246,802
Weighted average exercise price of options outstanding (in Dollars per share)	$ 20.58
Weighted average remaining contractual term of options outstanding	6 years 240 days
Aggregate intrinsic value of options outstanding (in Dollars)	2,310
Number of options exercisable	121,662
Weighted average exercise price of options exercisable (in Dollars per share)	$ 18.68
Weighted average remaining contractual term of options exercisable	5 years 193 days
Aggregate intrinsic value of options exercisable (in Dollars)	$ 1,360