Share-Based Compensation (Tables)

3 Months Ended

12 Months Ended

Mar. 31, 2018

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of Incentive Unit Activity

he following table summarizes the Company’s incentive unit activity since December 31, 2016:

	Number of Units			Weighted Average Strike Price		Weighted Average Contractual Term		Aggregate Intrinsic Value
						(in years)		(in thousands)
Outstanding as of December 31, 2016		413,266		$	2.75		9.1	$	779
Granted		9,132			1.28		—		—
Exercised		—			—		—		—
Forfeited		(19,541	)		4.99		—		—
Cancelled		(402,857	)		2.62		—		—
Outstanding as of December 31, 2017		—		$	—		—	$	—

Summary of Assumptions Used to Determine Fair Value of Incentive Unit and Stock Option Awards Granted to Employees and Directors

The assumptions that the Company used in the Black-Scholes option-pricing model to determine the fair value of incentive unit and stock option awards granted to employees and directors were as follows, presented on a weighted average basis:

	Year Ended December 31,
	2017			2016			2015
Risk-free interest rate		2.0	%		1.3	%		1.5	%
Expected term (in years)		6.1			6.3			6.3
Expected volatility		77.1	%		76.5	%		62.6	%
Expected dividend yield		0.0	%		0.0	%		0.0	%

Summary of Stock Option Activity

The following table summarizes stock option activity during 2017:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Contractual Term		Aggregate Intrinsic Value
						(in years)		(in thousands)
Outstanding as of December 31, 2016		—		$	—		—	$	—
Granted		2,012,106			7.24		—		—
Exercised		—			—		—		—
Forfeited		(810	)		5.90		—		—
Cancelled		—			—		—		—
Outstanding as of December 31, 2017		2,011,296		$	7.24		9.38	$	9,074
Outstanding as of December 31, 2017—vested and expected to vest		2,011,296		$	7.24		9.38	$	9,074
Exercisable at December 31, 2017		357,494		$	5.90		9.29	$	2,091

Summary of Share-Based Compensation Expense

The Company recorded share-based compensation expense in the following expense categories of its consolidated statements of operations and comprehensive loss (in thousands):

	Three Months Ended March 31,
	2018		2017
Research and development expenses	$	250	$	23
General and administrative expenses		364		39
Total	$	614	$	62

The Company recorded share-based compensation expense, for both incentive units and stock options in the following expense categories of its consolidated statements of operations and comprehensive loss (in thousands):

	Year Ended December 31,
	2017		2016		2015
Research and development expenses	$	371	$	66	$	13
General and administrative expenses		1,056		114		8
Total	$	1,427	$	180	$	21