Stock-based Compensation (Tables)

6 Months Ended

Jun. 30, 2020

Stock-based Compensation

Summary of stock-based compensation

	Three months ended June 30,				Six months ended June 30,
	2020		2019		2020		2019
Research and development expenses	$	984	$	514	$	1,754	$	1,081
Selling, general and administrative expenses		4,600		3,648		8,781		7,344
Total stock-based compensation expense	$	5,584	$	4,162	$	10,535	$	8,425

Summary of performance share units activity

		Weighted-Average
	Shares	Grant Date Fair Value
Outstanding at December 31, 2019	99,400	$	15.90
Granted	187,978		28.49
Vested	—		—
Forfeited	—		—
Performance adjustment	(4,155)		15.90
Outstanding at June 30, 2020	283,223	$	24.26

Summary of restricted stock units activity

		Weighted-Average
	Shares	Grant Date Fair Value
Outstanding at December 31, 2019	849,679	$	17.10
Granted	762,607		21.37
Vested	(278,741)		17.97
Forfeited	(16,025)		18.87
Outstanding at June 30, 2020	1,317,520	$	19.37

Summary of stock option activity

				Weighted-
			Weighted-	Average
			Average	Remaining		Aggregate
			Exercise Price	Contractual		Intrinsic
	Shares		per Share	Term (in years)		Value
Outstanding at December 31, 2019	3,955,887	$	16.00	7.5	$	21,257
Granted	701,249		21.39
Exercised	(587,135)		10.36
Cancelled	(98,551)		20.69
Outstanding at June 30, 2020	3,971,450	$	17.67	7.7	$	7,866
Exercisable at June 30, 2020	2,123,646	$	16.95	6.7	$	5,058

Schedule of fair value assumption using Black-Scholes option-pricing model

	Six months ended June 30,
	2020		2019
Risk-free interest rate	1.3	%	2.6	%
Volatility	66.1	%	63.3	%
Expected term (years)	6.1		6.1
Expected dividend yield	—	%	—	%