Stockholders' Equity - Stock-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock-based compensation
Stock-based compensation expense, net of $0 tax in 2016, 2017 and 2018	$ 3,880	$ 5,307	$ 8,423
Stock-based compensation expense, tax	$ 0	$ 0	$ 0
2016 Plan
Stock-based compensation
Number of shares available for future grant	2,054,993
2016 Plan | Stock options
Stock-based compensation
Vesting period	3 years
Contractual term	10 years
Number of Shares
Outstanding at the beginning of the period (in shares)	8,699,677
Granted (in shares)	2,183,691
Exercised (in shares)	(58,602)
Forfeited or expired (in shares)	(1,703,101)
Outstanding at the end of the period (in shares)	9,121,665	8,699,677
Exercisable at the end of the period (in shares)	6,246,982
Vested and expected to vest at the end of the period (in shares)	9,121,665
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 8.06
Granted (in dollars per share)	2.19
Exercised (in dollars per share)	1.79
Forfeited or expired (in dollars per share)	10.07
Outstanding at the end of the period (in dollars per share)	6.32	$ 8.06
Exercisable at the end of the period (in dollars per share)	8.31
Vested and expected to vest at the end of the period (in dollars per share)	$ 6.32
Additional option disclosures
Outstanding at the end of the period, weighted average remaining contractual term	5 years 9 months 26 days
Exercisable at the end of the period, weighted average remaining contractual term	4 years 6 months 7 days
Vested and expected to vest at the end of the period, weighted average remaining contractual term	5 years 9 months 26 days
Outstanding at the end of the period, aggregate intrinsic value	$ 1,909
Exercisable at the end of the period, aggregate intrinsic value	812
Vested and expected to vest at the end of the period, aggregate intrinsic value	1,909
Total unrecognized compensation cost related to non-vested shares	$ 1,900
Weighted average period over which the total unrecognized compensation cost related to non-vested shares is expected to be recognized	1 year 5 months 12 days
Total fair value of shares vested	$ 1,600
Weighted-average assumption used for grants
Dividend yield	0.00%	0.00%	0.00%
Expected volatility			63.61%
Expected volatility, minimum	57.30%	70.20%
Expected volatility, maximum	61.50%	74.60%
Risk-free interest rate			2.05%
Risk-free interest rate, minimum	2.11%	2.70%
Risk-free interest rate, maximum	2.53%	2.71%
Expected life	6 years	6 years	6 years
Stock-based compensation
Weighted-average grant date fair values of options granted (in dollars per share)	$ 1.28	$ 0.88	$ 1.67
Exercised during the period, aggregate intrinsic value	$ 100	$ 0
Stock-based compensation expense	$ 2,200	$ 2,000	$ 2,200
2016 Plan | Stock options | Vesting over the first year
Stock-based compensation
Vesting percentage	34.00%
2016 Plan | Stock options | Vesting over the second year
Stock-based compensation
Vesting percentage	33.00%
2016 Plan | Stock options | Vesting over the third year
Stock-based compensation
Vesting percentage	33.00%
Asset impairments and other charges
Stock-based compensation
Stock-based compensation expense, net of $0 tax in 2016, 2017 and 2018			$ 300