Stockholders' Equity - Summary of Warrant Activity (Details) shares in Thousands	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Common Shares Issuable upon Exercise
Outstanding, beginning balance (in shares) | shares	236
Issued (in shares) | shares	342
Exercised (in shares) | shares	(35)
Cancelled (in shares) | shares	(107)
Outstanding, ending balance (in shares) | shares	437
Exercisable at balance sheet date (in shares) | shares	225
Weighted Average Exercise Price
Outstanding, beginning balance (in usd per share) | $ / shares	$ 117.30
Issued (in usd per share) | $ / shares	12.30
Exercised (in usd per share) | $ / shares	44.40
Cancelled (in usd per share) | $ / shares	119.70
Outstanding, ending balance (in usd per share) | $ / shares	20.70
Exercisable at balance sheet date (in dollars per share) | $ / shares	$ 30.30