Note 7 - Share Based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Notes Tables

Share-based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity [Table Text Block]

	Number of shares			Weighted average grant date fair value
				$
Outstanding at December 31, 2016		-			-
Granted		1,141,477			20.76
Vested		(434,615	)		22.19
Forfeited		(318,700	)		19.80
Outstanding at December 31, 2017		388,162			19.93
Granted		9,815			19.50
Vested		(147,727	)		19.88
Forfeited		(95,000	)		19.96
Outstanding at December 31, 2018		155,250			19.94
Expected to vest at December 31, 2018		125,250			19.97

Share-based Payment Arrangement, Option, Activity [Table Text Block]

	Numbers of options		Weighted average exercise price		Weighted average grant date fair value		Weighted average remaining contractual term		Average intrinsic value
				$		$		Years		$
Outstanding at December 31, 2016		-		-
Granted		343,000		29.00		19.91
Outstanding at December 31, 2017		343,000		29.00				9.98		27
Granted		130,000		25.08		14.49
Forfeited		7,100		29.00		19.91
Outstanding at December 31, 2018		465,900		27.91				9.12		-
Exercisable as of December 31, 2018		335,900		29.00				8.98		-
Vested and expected to vest at December 31, 2018		441,400		28.00				9.11		-

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	December 31,
	2017			2018
Fair value of ordinary share		34.00			24.87	~	26.09
Risk-free interest rate		2.28	%		2.73%	~	2.89%
Expected term (years)		5.5			5.9	~	6.2
Expected volatility		60	%			60%
Expected dividend yield		0	%			0%
Contractual life (years)		10				10

Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]

	December 31,
	2017		2018
Research and development		17,753		6,821
General and administrative		4,930		(261	)
Total		22,683		6,560