Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

Summary of stock-based compensation expense

During the years ended December 31, 2018, 2017 and 2016, the Company recorded stock-based compensation expense, which was allocated as follows in the consolidated statements of operations and comprehensive (loss) income (in thousands):



	Year Ended December 31,
	2018		2017		2016
Research and development expense	$	505	$	404	$	1,455
General and administrative expense	778		977		2,558
	$	1,283	$	1,381	$	4,013

Summary of assets and liabilities measured at fair value on a recurring basis

The following table summarizes the assets and liabilities measured at fair value on a recurring basis at December 31, 2018 (in thousands):



Description	December 31, 2018		Active Markets (Level 1)		Observable Inputs (Level 2)		Unobservable Inputs (Level 3)
Assets:
Cash and cash equivalents	$	50,422	$	50,422	$	—	$	—
Restricted cash	20		20		—		—
Total assets	$	50,442	$	50,442	$	—	$	—
Liabilities:
Contingent consideration	48,400		—		—		48,400
Total liabilities	$	48,400	$	—	$	—	$	48,400

The following table summarizes the assets and liabilities measured at fair value on a recurring basis at December 31, 2017 (in thousands):



Description	December 31, 2017		Active Markets (Level 1)		Observable Inputs (Level 2)		Unobservable Inputs (Level 3)
Assets:
Cash and cash equivalents	$	14,680	$	14,680	$	—	$	—
Restricted cash	10		10		—		—
Total assets	$	14,690	$	14,690	$	—	$	—
Liabilities:
Contingent consideration	39,600		—		—		39,600
Total liabilities	$	39,600	$	—	$	—	$	39,600

Business acquisition contingent consideration liability

The following table sets forth a summary of changes in the fair value of the Company's contingent consideration liability, which represented a recurring measurement classified within Level 3 of the fair value hierarchy, wherein fair value was estimated using significant unobservable inputs (in thousands):



Beginning balance, January 1, 2018	$	39,600
Loss from change in fair value of contingent consideration	8,800
Ending balance, December 31, 2018	$	48,400

Summary of common stock equivalents using the treasury stock method

The following common stock equivalents, using the treasury-stock method, were included in the calculation of diluted net (loss) income per share for the periods indicated.



	Year ended December 31,
	2018	2017	2016
Stock options	—	—	650,109

Summary of common stock equivalents excluded from calculation of diluted net (loss) income per share

The following common stock equivalents were excluded from the calculation of diluted net (loss) income per share for the periods indicated because including them would have had an anti-dilutive effect or the exercise prices were greater than the average market price of the common shares.



	Year ended December 31,
	2018	2017	2016
Stock options	3,941,947	2,695,796	1,374,359
Unvested restricted stock	—	4,430	22,150
Restricted stock units	—	—	3,333
Common stock warrants	9,257,632	10,055,000	926,840
	13,199,579	12,755,226	2,326,682