Note 6 - Share-based Compensation - Stock Option Activity (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2015 USD ($) $ / shares shares
Common Class A [Member]
Outstanding at December 31, 2014, number of options (in shares)	1,324,520
Outstanding at December 31, 2014, weighted average exercise price (in dollars per share) | $ / shares	$ 11.07
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	225,306
Granted, weighted average exercise price (in dollars per share) | $ / shares	$ 13.83
Exercised, number of options (in shares)	(25,983)
Exercised, weighted average exercise price (in dollars per share) | $ / shares	$ 6.30
Exercised, aggregate intrinsic value | $	$ 179
Forfeited, number of options (in shares)	(56,105)
Forfeited, weighted average exercise price (in dollars per share) | $ / shares	$ 13.12
Outstanding at June 30, 2015, number of options (in shares)	1,467,738
Outstanding at June 30, 2015, weighted average exercise price (in dollars per share) | $ / shares	$ 11.50
Outstanding at June 30, 2015, weighted average remaining contractual term	6 years 36 days
Outstanding at June 30, 2015, aggregate intrinsic value | $	$ 2,774
Exercisable, number of options (in shares)	1,059,990
Exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 11.04
Exercisable, weighted average remaining contractual term	5 years 149 days
Exercisable, aggregate intrinsic value | $	$ 2,478
Common Class B [Member]
Outstanding at December 31, 2014, number of options (in shares)	213,470
Outstanding at December 31, 2014, weighted average exercise price (in dollars per share) | $ / shares	$ 24.32
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	37,551
Granted, weighted average exercise price (in dollars per share) | $ / shares	$ 34.85
Exercised, number of options (in shares)	(4,330)
Exercised, weighted average exercise price (in dollars per share) | $ / shares	$ 14.82
Exercised, aggregate intrinsic value | $	$ 89
Forfeited, number of options (in shares)	(9,018)
Forfeited, weighted average exercise price (in dollars per share) | $ / shares	$ 27.61
Outstanding at June 30, 2015, number of options (in shares)	237,673
Outstanding at June 30, 2015, weighted average exercise price (in dollars per share) | $ / shares	$ 26.04
Outstanding at June 30, 2015, weighted average remaining contractual term	6 years 58 days
Outstanding at June 30, 2015, aggregate intrinsic value | $	$ 2,047
Exercisable, number of options (in shares)	170,663
Exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 24.94
Exercisable, weighted average remaining contractual term	5 years 171 days
Exercisable, aggregate intrinsic value | $	$ 1,703