Collaboration and Feasibility Agreements - Additional Information (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended		12 Months Ended
	Oct. 10, 2016	Jan. 31, 2015	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2014	Dec. 31, 2016
Collarboration and Feasibility Agreements
Revenue recognized				$ 42
Feasibility Agreement | Biotechnology
Collarboration and Feasibility Agreements
Potential agreement revenue					$ 700
Non-Refundable revenue entitled to receive on milestone achievement					250
Maximum revenue that could be recognized					$ 450
Payment received on milestone achievement		$ 250
Non-Refundable revenue			$ 500
Revenue recognized			0	$ 42
Deferred revenue			0			$ 0
Accounts receivable			$ 0			$ 0
Collaboration Agreement | Regeneron
Collarboration and Feasibility Agreements
Payment receivable upon exercise of option	$ 10,000
Collaboration Agreement | Regeneron | Maximum
Collarboration and Feasibility Agreements
Reimbursable clinical development costs	25,000
Potential increase in reimbursable clinical development costs	5,000
Potential payment receivable per Licensed Product upon the achievement of specified development and regulatory milestones	145,000
Potential payment receivable per Licensed Product upon first commercial sale of such Licensed Product	100,000
Potential payment receivable due for achievement of specified sales milestones for all Licensed Products	$ 50,000