Note 4 - Summary of Restricted Stock Unit Activity (Details) - Restricted Stock [Member]	6 Months Ended
	Jun. 30, 2016 $ / shares shares
Unvested balance (in shares) | shares	643,506
Unvested balance (in dollars per share) | $ / shares	$ 23.38
Granted (in shares) | shares	829,744
Granted (in dollars per share) | $ / shares	$ 17.37
Vested (in shares) | shares	(126,097)
Vested (in dollars per share) | $ / shares	$ 24.55
Forfeited (in shares) | shares	(25,600)
Forfeited (in dollars per share) | $ / shares	$ 18.88
Unvested balance (in shares) | shares	1,321,553
Unvested balance (in dollars per share) | $ / shares	$ 19.58