Organization and Significant Accounting Policies - Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Total cost	$ 32,504	$ 32,210
Less accumulated depreciation	(26,528)	(25,938)
Total net book value	5,976	6,272
Land
Total cost	$ 1,050	1,050
Building
Depreciable Life	39 years
Total cost	$ 3,950	3,950
Building and leasehold improvements
Total cost	$ 3,242	3,264
Building and leasehold improvements \| Minimum
Depreciable Life	3 years
Building and leasehold improvements \| Maximum
Depreciable Life	39 years
Field equipment
Total cost	$ 19,541	19,251
Field equipment \| Minimum
Depreciable Life	3 years
Field equipment \| Maximum
Depreciable Life	4 years
Computer equipment and software
Total cost	$ 3,154	3,124
Computer equipment and software \| Minimum
Depreciable Life	2 years
Computer equipment and software \| Maximum
Depreciable Life	3 years
Furniture and fixtures
Total cost	$ 1,535	1,539
Furniture and fixtures \| Minimum
Depreciable Life	3 years
Furniture and fixtures \| Maximum
Depreciable Life	10 years
Vehicles
Depreciable Life	5 years
Total cost	$ 32	$ 32

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

+ References

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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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