Stock Incentive Plans - Stock Option Plan Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Stock options
Outstanding at beginning of year (in shares)	283,277
Granted (in shares)	213,384
Exercised (in shares)	(291)
Cancelled or forfeited (in shares)	(62,981)
Outstanding at end of year (in shares)	433,389	283,277
Vested and Exercisable to vest at end of year (in shares)	168,566
Weighted-Average Exercise Price
Outstanding at beginning of year (in dollars per share)	$ 45.42
Granted (in dollars per share)	9.84
Exercised (in dollars per share)	12.40
Cancelled or forfeited (in dollars per share)	37.64
Outstanding at end of year (in dollars per share)	29.05	$ 45.42
Vested and Exercisable at end of year (in dollars per share)	$ 50.91
Weighted Average Remaining Contractual Term (years)
Outstanding at end of year	7 years 11 months 19 days	7 years 9 months
Vested and Exercisable at end of year	6 years 3 months 22 days
Aggregate Intrinsic Value
Outstanding at the beginning of the year	$ 216
Outstanding at the end of the year		$ 216
Weighted average of the assumptions used to compute employee stock based compensation
Expected dividend yield (as a percent)	0.00%	0.00%
Stock options
Unrecognized stock-based compensation expense
Intrinsic value of options exercised	$ 1	$ 40
Adjusted fair value of options vested	$ 1,700	$ 2,200
Weighted average grant date fair value of options granted (in dollars per share)	$ 6.64	$ 8.48
Unrecognized compensation expense related to unvested stock option awards	$ 2,300
Weighted-average amortization period over which cost is expected to be recognized	1 year 8 months 12 days
Minimum
Weighted average of the assumptions used to compute employee stock based compensation
Weighted-average expected volatility (as a percent)	73.70%	76.10%
Expected term (in years)	5 years 9 months	6 years 3 months
Risk-free interest rate (as a percent)	2.67%	2.00%
Maximum
Weighted average of the assumptions used to compute employee stock based compensation
Weighted-average expected volatility (as a percent)	76.90%	81.90%
Expected term (in years)	6 years 3 months	9 years 9 months 7 days
Risk-free interest rate (as a percent)	2.84%	2.38%

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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Weighted average price of options that were either forfeited or expired.

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Gross number of share options (or share units) granted during the period.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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Number of share options (or share units) exercised during the current period.

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