Stockholders' Equity - ESPP (Details) - Employee Stock Purchase Plan - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Employee Stock Purchase Plan (Abstract)
Shares available for issuance under ESPP	825,154	911,725
Number of shares purchased under ESPP	86,571
Average purchase price of shares under ESPP	$ 2.68