Stock Based Compensation - Summary of Stock Options Outstanding (Details) - $ / shares	3 Months Ended	12 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
STOCK-BASED COMPENSATION
Number of stock options outstanding, Beginning of period	19,170	5,723	5,723	110,828
Number of stock options outstanding, Granted			812,689	189,164
Number of stock options outstanding, Expired	(280)	(112)	(140,374)	(13,818)
Number of stock options outstanding, Canceled or forfeited
Number of stock options outstanding, End of period	18,890	5,611	19,170	5,723
Number of stock options Exercisable, End of period	18,890	1,828	958,489	97,010
Weighted average exercise price, Beginning of period	$ 79.78	$ 276.50	$ 276.50	$ 18.24
Weighted average exercise price, Granted			0.98	1.40
Weighted average exercise price, Expired	179.68	624.00	5.97	50.88
Weighted average exercise price, Canceled or forfeited
Weighted average exercise price, End of period	78.21	269.50	79.78	276.50
Weighted average exercise price Exercisable, End of period	$ 78.21	$ 682.50	$ 1.60	$ 13.59

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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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.

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

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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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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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