Share-based Compensation - Summary of Company's Stock Option Activity (Details) - $ / shares	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Shares
Outstanding at beginning of period (in shares)	7,160,861	6,989,856
Granted (in shares)	0	662,769
Exercised (in shares)	0	(274,037)
Forfeited (in shares)	0	(60,293)
Expired (in shares)	(93,269)	(157,434)
Outstanding at end of period (in shares)	7,067,592	7,160,861
Eligible for exercise (in shares)	6,613,099
Weighted Average Exercise Price
Outstanding at beginning of period (in usd per share)	$ 6.51	$ 6.57
Granted (in usd per share)	0	5.45
Exercised (in usd per share)	0	4.37
Forfeited (in usd per share)	0	5.50
Expired (in usd per share)	5.47	9.00
Outstanding at end of period (in usd per share)	6.52	$ 6.51
Eligible for exercise (in usd per share)	$ 6.59

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

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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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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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 per share amount at which grantees can acquire shares of common stock by exercise of options.

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

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