Stock Compensation - Restricted Stock and Performance Share Grants - Compensation Costs (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	3 Months Ended	6 Months Ended
Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2013 Executive Officer	Mar. 31, 2013 Executive Officer	Jun. 30, 2014 1998 Plan	Jun. 30, 2013 1998 Plan	Jun. 30, 2014 NDSI Plan	Jun. 30, 2013 NDSI Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation costs, expensed			$ (2,271)	$ (485)	$ 1,148	$ (952)	$ 414	$ 384
Stock compensation costs, capitalized					46	208
Stock compensation costs	$ 1,608	$ (360)			$ 1,194	$ (744)

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 14.F)

-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(1)(i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 14

-Section F

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