Stock Based Compensation Stock Based Compensation (Unrecognized compensation costs) (Details) $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($)
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Unrecognized compensation cost	$ 13,833
Restricted stock units [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Unrecognized compensation cost	$ 8,693
Weighted average remaining period of expense recognition (in years)	1 year 6 months
Performance-based restricted stock units [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Unrecognized compensation cost	$ 5,140
Weighted average remaining period of expense recognition (in years)	2 years 4 months 12 days

Unrecognized cost of unvested share-based compensation awards.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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