Stock Compensation - Restricted Stock and Performance Share Grants - Compensation Costs (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock Compensation Costs	$ 3,048	$ 2,225
1998 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation costs, expensed	2,179	1,311
Stock compensation costs, capitalized	649	633
Total Stock Compensation Costs	2,828	1,944
NDSI Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation costs, expensed	$ 220	$ 281

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of additional cost recognized for award under share-based payment arrangement from occurrence of event accelerating recognition of cost.

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