Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Number of shares
Outstanding at beginning of period (in shares)	286,712
Granted (in shares)	0
Exercised (shares)	0
Forfeited (in shares)	0
Expired (in shares)	(385)
Outstanding at end of period (in shares)	286,327	286,712
Exercisable at end of period (in shares)	181,915
Weighted- average exercise price
Outstanding at beginning of period (in dollars per share)	$ 46.01
Granted (in dollars per share)	0.00
Exercised (in dollars per share)	0.00
Forfeited (in dollars per share)	0.00
Expired (in dollars per share)	18.05
Outstanding at end of period (in dollars per share)	46.04	$ 46.01
Exercisable at end of period (in dollars per share)	$ 68.25
Additional disclosures
Weighted-average remaining contractual term (in years), outstanding	6 years 9 months	7 years
Weighted-average remaining contractual term (in years), exercisable	5 years 9 months
Aggregate intrinsic value, outstanding	$ 0	$ 0
Aggregate intrinsic value, exercisable	$ 0

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

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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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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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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 option holders acquired shares when converting their stock options into shares.

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