Stockholders' Equity - Restricted Stock Units (Details)	6 Months Ended
	Jun. 30, 2018 $ / shares shares
Restricted Stock Units
Outstanding at beginning of period (in shares) | shares	248,512
Granted (in shares) | shares	25,035
Canceled/forfeited (in shares) | shares	(21,428)
Outstanding at end of period (in shares) | shares	242,119
Weighted Average Grant Date Fair Value
Outstanding at beginning of period (in dollars per share) | $ / shares	$ 5.76
Granted (in dollars per share) | $ / shares	2.46
Canceled/forfeited (in dollars per share) | $ / shares	9.94
Outstanding at end of period (in dollars per share) | $ / shares	$ 4.46
Weighted Average Remaining Contractual Life (in years)
Outstanding at end of period	7 years 9 months 18 days
Restricted Stock Units
Restricted Stock Units
Outstanding at beginning of period (in shares) | shares	306,142
Granted (in shares) | shares	503,183
Released (in shares) | shares	(180,293)
Canceled/forfeited (in shares) | shares	(24,120)
Outstanding at end of period (in shares) | shares	604,912
Weighted Average Grant Date Fair Value
Outstanding at beginning of period (in dollars per share) | $ / shares	$ 3.37
Granted (in dollars per share) | $ / shares	2.44
Released (in dollars per share) | $ / shares	3.18
Canceled/forfeited (in dollars per share) | $ / shares	3.51
Outstanding at end of period (in dollars per share) | $ / shares	$ 2.65
Weighted Average Remaining Contractual Life (in years)
Outstanding at end of period	2 years 8 months 12 days