Stock-Based Compensation - Other Selected Information (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock-Based Compensation
Aggregate fair value of stock option awards vested	$ 1,183	$ 374	$ 644
Aggregate intrinsic value of outstanding stock option awards	954	1,270	5,503
Aggregate intrinsic value of stock option awards exercised	$ 5,533	$ 1,713	$ 748
Weighted-average grant-date fair value per share of stock option awards granted (usd per share)	$ 3.21	$ 1.91	$ 1.13
Cash proceeds received from stock option awards exercised	$ 6,749	$ 1,845	$ 699
Stock option awards
Stock-Based Compensation
Unrecognized compensation cost related to non-vested stock option awards	$ 3,390
Weighted-average period over which unrecognized compensation cost is expected to be recognized	2 years 7 months 17 days

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of cost to be recognized for option under share-based payment arrangement.

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Amount of cash inflow from exercise of option under share-based payment arrangement.

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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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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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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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