Share-based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Estimated Weighted Average Grant Date Fair Value per Share

The Company granted options for 469,600 and 487,700 shares of common stock in the years ended December 31, 2017 and 2016, respectively. The fair values of employee stock options granted in the years ended December 31, 2017 and 2016 were estimated at the date of grant using the Black-Scholes model with the following assumptions and had the following estimated weighted average grant date fair value per share:

	Years Ended December 31,
	2017			2016
Expected term	5.8 years			5.7 years
Expected volatility		73	%		72	%
Risk-free interest rate		1.99	%		1.29	%
Expected dividend yield		0	%		0	%
Weighted-average grant date fair value per share	$	1.60		$	2.01

Summary of Stock Option Activities

A summary of ARCA’s stock option activities for the years ended December 31, 2017 and 2016, and related information as of December 31, 2017, is as follows:

	Options Outstanding
	Number of Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Options outstanding - December 31, 2015		161,278		$	18.30
Granted		487,700			3.22
Exercised		—			—
Forfeited and cancelled		(19,349	)		28.70
Options outstanding - December 31, 2016		629,629		$	6.30		8.86	$	25
Granted		469,600			2.54
Exercised		—			—
Forfeited and cancelled		(487,254	)		3.05
Options outstanding - December 31, 2017		611,975		$	6.00		8.14	$	—
Options exercisable - December 31, 2017		348,961		$	8.27		7.59	$	—
Options vested and expected to vest - December 31, 2017		611,101		$	6.00		8.14	$	—

Summary of RSU Activity

A summary of RSU activity for the years ended December 31, 2017 and 2016 is presented below:

	Restricted Stock Units Outstanding
	Number of Shares			Weighted Average Grant Date Fair Value
RSUs outstanding - December 31, 2015		62,359		$	8.36
Granted		—			—
Vested and released		(31,149	)		8.85
Forfeited and cancelled		(471	)		4.69
RSUs outstanding - December 31, 2016		30,739		$	7.91
Granted		—			—
Vested and released		(15,171	)		7.94
Forfeited and cancelled		(400	)		6.03
RSUs outstanding - December 31, 2017		15,168		$	7.94

Summary of Non-cash, Share-based Compensation Expense

For the years ended December 31, 2017 and 2016, the Company recognized the following non-cash, share-based compensation expense (in thousands):

	Years Ended
	December 31,
	2017		2016
Research and development	$	169	$	167
General and administrative		289		409
Total	$	458	$	576