Stockholders' Equity - Restricted Stock Units (Details)	9 Months Ended
	Sep. 30, 2018 $ / shares shares
Restricted Stock Units
Outstanding at beginning of period (in shares) | shares	248,512
Granted (in shares) | shares	100,746
Canceled/forfeited (in shares) | shares	(43,787)
Outstanding at end of period (in shares) | shares	295,471
Weighted Average Grant Date Fair Value
Outstanding at beginning of period (in dollars per share) | $ / shares	$ 5.76
Granted (in dollars per share) | $ / shares	1.97
Canceled/forfeited (in dollars per share) | $ / shares	7.17
Outstanding at end of period (in dollars per share) | $ / shares	$ 3.78
Weighted Average Remaining Contractual Life (in years)
Outstanding at end of period	7 years 6 months
Restricted Stock Units
Restricted Stock Units
Outstanding at beginning of period (in shares) | shares	306,142
Granted (in shares) | shares	553,657
Released (in shares) | shares	(213,795)
Canceled/forfeited (in shares) | shares	(76,950)
Outstanding at end of period (in shares) | shares	569,054
Weighted Average Grant Date Fair Value
Outstanding at beginning of period (in dollars per share) | $ / shares	$ 3.37
Granted (in dollars per share) | $ / shares	2.38
Released (in dollars per share) | $ / shares	3.14
Canceled/forfeited (in dollars per share) | $ / shares	2.99
Outstanding at end of period (in dollars per share) | $ / shares	$ 2.55
Weighted Average Remaining Contractual Life (in years)
Outstanding at end of period	2 years