License Agreements and Grants - Arizona Commerce Authority and R&D Refundable Tax Credit Program (Details)	1 Months Ended		12 Months Ended
	Jan. 31, 2018 USD ($)	Aug. 31, 2012 USD ($) job milestone	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Research and Development [Abstract]
Arizona Commerce Authority grant		$ 1,000,000	$ 1,000,000
Number of milestones | milestone		4
Qualified jobs created, milestone 1 | job		15
Qualified jobs created, milestone 2 | job		30
Qualified jobs created, milestone 3 | job		40
Qualified jobs created, milestone 4 | job		65
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Deferred revenue recognized			0	$ 114,000
Offset to research and development project			$ 0	$ 1,200,000	$ 647,000
Subsequent Event
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Deferred revenue recognized	$ 1,000,000
Minimum
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Capital investment milestone		$ 4,500,000
Grant related minimum annual wages		$ 63,000
Percent of company paid premiums		65.00%