Inventory (Narrative) (Details) $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($) a Building	Dec. 31, 2017 USD ($)
Real Estate [Line Items]
Purchase of inventory	$ 2,235	$ (93)
Alabama [Member]
Real Estate [Line Items]
Area of campus \| a	110
Number of buildings \| Building	3
Purchase of inventory	$ 2,300

The increase (decrease) during the reporting period in the aggregate value of all inventory held by the reporting entity, associated with underlying transactions that are classified as operating activities.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

Name:	us-gaap_IncreaseDecreaseInInventories
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration