Property and Equipment - Narrative (Details)	12 Months Ended
Dec. 31, 2017
Property, plant and equipment [abstract]
Percentage increase in discount rate used in impairment assessments	5.00%
Percentage decrease in discount rate used in impairment assessments	5.00%

Sensitivity Analysis, Decrease In Discount Rate Used For Assets With Significant Risk Of Material Adjustments, Impact On Impairment Loss, Percent

No definition available.

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Namespace Prefix:	tga_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration