Stockholders' Equity - ESPP (Details) - Employee Stock Purchase Plan - $ / shares	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Jan. 01, 2017
Employee Stock Purchase Plan (Abstract)
Shares available for issuance under ESPP	787,918	787,918	825,154
Number of shares purchased under ESPP	0	37,236
Average purchase price of shares under ESPP	$ 1.30	$ 1.30