Stock-Based Compensation - Ranges of Outstanding and Exercisable Options (Details) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
$20.50 - $43.59
Options Outstanding
Number Outstanding (in shares) | shares	20
Weighted Average Remaining Contractual Life	6 years 9 months 29 days
Weighted Average Exercise Price (in dollars per share)	$ 20.89
Options Exercisable
Number Exercisable (in shares) | shares	15
Weighted Average Exercise Price (in dollars per share)	$ 21.02
Options
Options Outstanding
Vested and expected to vest, Number Outstanding | shares	281
Vested and expected to vest, Weighted Average Remaining Contractual Life (in Years)	7 years 1 month 2 days
Vested and expected to vest, Weighted Average Exercise Price	$ 5.07
Exercisable, Number Outstanding | shares	73
Exercisable, Weighted Average Remaining Contractual Life	8 years 1 month 24 days
Exercisable, Weighted Average Exercise Price	$ 10.55
Aggregate Intrinsic Value [Abstract]
Vested and expected to vest, Aggregate Intrinsic Value | $	$ 50
Options | $0.75 - $2.35
Exercise price range
Lower range limit (in dollars per share)	$ 0.75
Upper range limit (in dollars per share)	$ 2.35
Options Outstanding
Number Outstanding (in shares) | shares	160
Weighted Average Remaining Contractual Life	5 years 9 months 18 days
Weighted Average Exercise Price (in dollars per share)	$ 0.75
Aggregate Intrinsic Value [Abstract]
Options Outstanding, Aggregate Intrinsic Value | $	$ 58
Options | $2.36 - $7.19
Exercise price range
Lower range limit (in dollars per share)	$ 2.36
Upper range limit (in dollars per share)	$ 7.19
Options Outstanding
Number Outstanding (in shares) | shares	11
Weighted Average Remaining Contractual Life	8 years 7 months 28 days
Weighted Average Exercise Price (in dollars per share)	$ 4.92
Options Exercisable
Number Exercisable (in shares) | shares	6
Weighted Average Exercise Price (in dollars per share)	$ 5.18
Options | $7.20 - $20.49
Exercise price range
Lower range limit (in dollars per share)	7.20
Upper range limit (in dollars per share)	$ 20.49
Options Outstanding
Number Outstanding (in shares) | shares	114
Weighted Average Remaining Contractual Life	8 years 7 months 21 days
Weighted Average Exercise Price (in dollars per share)	$ 7.20
Options Exercisable
Number Exercisable (in shares) | shares	51
Weighted Average Exercise Price (in dollars per share)	$ 7.20
Options | $20.50 - $43.59
Exercise price range
Lower range limit (in dollars per share)	20.50
Upper range limit (in dollars per share)	43.59
Options | $44.60 - $46.19
Exercise price range
Lower range limit (in dollars per share)	44.60
Upper range limit (in dollars per share)	$ 46.19
Options Outstanding
Number Outstanding (in shares) | shares	1
Weighted Average Remaining Contractual Life	2 years 9 months 4 days
Weighted Average Exercise Price (in dollars per share)	$ 44.60
Options Exercisable
Number Exercisable (in shares) | shares	1
Weighted Average Exercise Price (in dollars per share)	$ 44.60
Options | $46.20 - $46.20
Exercise price range
Lower range limit (in dollars per share)	46.20
Upper range limit (in dollars per share)	$ 46.20
Options Outstanding
Number Outstanding (in shares) | shares	1
Weighted Average Remaining Contractual Life	6 years 1 month 17 days
Weighted Average Exercise Price (in dollars per share)	$ 46.20
Options Exercisable
Weighted Average Exercise Price (in dollars per share)	46.20
Options | $0.75 - $46.20
Exercise price range
Lower range limit (in dollars per share)	0.75
Upper range limit (in dollars per share)	$ 46.20
Options Outstanding
Number Outstanding (in shares) | shares	307
Weighted Average Remaining Contractual Life	7 years 7 days
Weighted Average Exercise Price (in dollars per share)	$ 4.81
Options Exercisable
Number Exercisable (in shares) | shares	73
Weighted Average Exercise Price (in dollars per share)	$ 10.55
Aggregate Intrinsic Value [Abstract]
Options Outstanding, Aggregate Intrinsic Value | $	$ 58