Summary of Stock Option Activity (Details) - $ / shares	6 Months Ended
Jun. 30, 2019
Stock Options Outstanding
Stock Options Outstanding, Beginning of year	3,424,755
Stock Options Outstanding, Exercised	(52,390)
Stock Options Outstanding, Cancelled	(21,875)
Stock Options Outstanding, End of year	3,350,490
Stock Options Outstanding, Exercisable	2,668,865
Weighted-Average Exercise Price
Weighted-Average Exercise Price, beginning of year	$ 11.49
Weighted Average Exercise Price, Exercised	9.06
Weighted Average Exercise Price, Cancelled	11.41
Weighted-Average Exercise Price, end of year	11.53
Weighted Average Exercise Price, Exercisable	$ 11.31

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

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

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