Stock Compensation - Restricted Stock and Performance Share Grants - Compensation Costs (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock Compensation Costs	$ 2,398	$ 1,930
1998 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation costs, expensed	1,411	1,346
Stock compensation costs, capitalized	622	236
Total Stock Compensation Costs	2,033	1,582
NDSI Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation costs, expensed	$ 365	$ 348

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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- Definition

Represents the compensation cost capitalized during the period arising from equity-based compensation arrangements (for example, shares of stock, units, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition

Additional share-based compensation cost recognized as a result of an occurrence of an event that accelerates its recognition.

+ References

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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.

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