Restructuring Costs (Tables)

12 Months Ended

Dec. 31, 2017

Restructuring and Related Activities [Abstract]

Summary of Restructuring Activities

The following table summarizes restructuring activities for the years ended December 31, 2017 and December 31, 2016:

	Contract Termination			Employee Termination			Asset Impairment			Total
	(in thousands)
Accrual balance at December 31, 2015	$	—		$	—		$	—		$	—
Restructuring costs charged to research and development expense		2,249			—			—			2,249
Restructuring costs charged to general and administrative expense		5			332			130			467
Non-cash charges		(681	)		—			(130	)		(811	)
Cash payments		(909	)		(233	)		—			(1,142	)
Accrual balance at December 31, 2016	$	664		$	99		$	—		$	763
Adjustments to research and development expense		(69	)		—			—			(69	)
Cash payments		(458	)		(99	)		—			(557	)
Accrual balance at December 31, 2017	$	137		$	—		$	—		$	137