Common Stock (Details) $ / shares in Units, $ in Thousands		1 Months Ended		3 Months Ended	12 Months Ended			26 Months Ended	29 Months Ended
	Apr. 05, 2019 USD ($)	Jan. 31, 2018 USD ($) $ / shares shares	Nov. 30, 2016 USD ($)	Mar. 31, 2019 USD ($) shares	Dec. 31, 2019 USD ($) Vote shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2018 USD ($) shares	Mar. 31, 2019 USD ($) shares	Feb. 25, 2019 USD ($)	Jan. 01, 2015 shares	Dec. 31, 2014 shares
Common Stock
Common stock, shares authorized | shares					100,000,000	100,000,000		100,000,000
Number of votes per share | Vote					1
Voting right description					Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company's stockholders.
Net proceeds from issuance of common stock					$ 37,537	$ 61,571	$ 29,238
Common Stock
Common Stock
Number of shares issued | shares					8,655,940	11,596,173	4,359,920
Common Stock | 2016 Sales Agreement
Common Stock
Maximum aggregate proceeds from offering			$ 40,000
Number of shares issued | shares				1,318,481		4,121,173		5,011,741	6,330,222
Net proceeds from issuance of common stock				$ 4,954		$ 26,824		$ 33,427	$ 38,381
Aggregate value available for issuance										$ 0
Common Stock | 2019 Sales Agreement
Common Stock
Maximum aggregate proceeds from offering	$ 50,000
Number of shares issued | shares					7,337,459
Net proceeds from issuance of common stock					$ 32,626
Common Stock | Follow-on Offering
Common Stock
Common stock, price per share | $ / shares		$ 5.00
Number of shares issued | shares		7,475,000
Net proceeds from issuance of common stock		$ 34,704
2014 Stock Incentive Plan | Common Stock
Common Stock
Common stock shares, reserved | shares					9,499,615						2,126,907	1,336,907