Note 11 - Stock-based Compensation - Stock Option and Restricted Stock (Details)	9 Months Ended
	Sep. 30, 2017 USD ($) $ / shares shares
Equity awards outstanding, options (in shares) | shares	210,023
Equity awards outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 59.77
Equity awards granted, options (in shares) | shares	513,464
Equity awards granted, weighted average exercise price (in dollars per share) | $ / shares	$ 2.69
Equity awards forfeited, cancelled or expired, options (in shares) | shares	(43,735)
Equity awards forfeited, cancelled or expired, weighted average exercise price (in dollars per share) | $ / shares	$ 164.12
Equity awards outstanding, options (in shares) | shares	679,752
Equity awards outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 9.94
Equity awards outstanding, contractual term (Year)	9 years 146 days
Equity awards exercisable, options (in shares) | shares	401,920
Equity awards exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 13.83
Equity awards exercisable, contractual term (Year)	9 years 47 days
Aggregate intrinsic value of awards exercisable, options | $
Restricted Stock [Member]
Equity awards outstanding, non-vested restricted stock (in shares) | shares	4,785
Equity awards outstanding, non-vested restricted stock weighted average grant date fair value (in dollars per share) | $ / shares	$ 37.42
Equity awards granted, non-vested restricted stock (in shares) | shares	(3,357)
Equity awards granted, non-vested restricted stock weighted average grant date fair value (in dollars per share) | $ / shares	$ 42.20
Equity awards forfeited, cancelled or expired, non-vested restricted stock (in shares) | shares	(1,428)
Equity awards forfeited, cancelled or expired, non-vested restricted stock weighted average grant date fair value (in dollars per share) | $ / shares	$ 26.18
Equity awards outstanding, non-vested restricted stock (in shares) | shares
Equity awards outstanding, non-vested restricted stock weighted average grant date fair value (in dollars per share) | $ / shares
Aggregate intrinsic value of outstanding awards, non-vested restricted stock | $