Securities Registrations and Sales Agreements - Sales and Purchase Agreements (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Oct. 08, 2015	Dec. 31, 2016
Securities Registrations and Sales Agreement
Aggregate offering price		$ 24,900
Lincoln Park | Purchase agreement
Securities Registrations and Sales Agreement
Issuance of stock (in shares)	5,645
Aggregate offering price	$ 15,000
Net proceeds from sales of common stock	$ 1,500
Business day limit (in shares)	666
Business day limit contingent upon the closing price of the stock (in shares)	1,666
Regular purchase, one day limit	$ 1,000
Beneficial ownership percentage (as a percent)	4.99%
Beneficial ownership percentage after 180 days (as a percent)	9.99%
Maximum shares issued as a percentage of shares outstanding (as a percent)	19.99%
Minimum average price per share (in dollars per share)	$ 233.40
Stock issued as consideration (in shares)	1,333