Contingently Issuable Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions		12 Months Ended
	Dec. 10, 2010	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value of Contingently Issuable Common Stock [Roll Forward]
Fair value of contingent payment, beginning balance		$ 12,200
Change in fair value of contingent consideration related to acquisition		(2,900)	$ (2,500)	$ 100
Fair value of contingent payment, ending balance		$ 9,300	$ 12,200
Nelix Milestones
Business Acquisition [Line Items]
Purchase price of common shares (in shares)		2.9
Contingently issuable shares (in shares)	10.2
Fair value of contingent payment	$ 28,200
PMA Milestone
Business Acquisition [Line Items]
Value of common shares	$ 15,000
Closing stock price (in USD per share)		$ 5.35
Hypothetical fair value		$ 15,200
PMA Milestone | Maximum
Business Acquisition [Line Items]
Closing stock price (in USD per share)	$ 4.50
Nellix
Business Acquisition [Line Items]
Purchase price of common shares (in shares)	3.2
Value of common shares	$ 19,400