Stock-Based Compensation - Stock option activity (Details) - $ / shares	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Options, Outstanding:
Beginning balance	34,123	143,224	216,859
Exercised	(26,784)	(108,201)	(72,535)
Forfeited	(750)	(900)
Expired			(1,100)
Ending balance	6,589	34,123	143,224
Options, Outstanding, Weighted Average Exercise Price:
Beginning balance	$ 14.69	$ 9.13	$ 8.80
Exercised	12.42	7.17	8.19
Forfeited	49.08	34.47
Expired			5.76
Ending balance	$ 19.99	$ 14.69	$ 9.13

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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- Definition

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.

+ References

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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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- Definition

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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No definition available.

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- Definition

Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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- Definition

Weighted average price at which option holders acquired shares when converting their stock options into shares.

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No definition available.

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- Definition

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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No definition available.

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- Definition

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

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No definition available.

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- Definition

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

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