Commitments and Contingencies - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Promissory notes as security for letters of credit	$ 120.6	$ 76.7

Debt Instrument, Collateral, Promissory Notes Provided as Collateral for Letters of Credit

No definition available.

Name:	gte_DebtInstrumentCollateralPromissoryNotesProvidedAsCollateralForLettersOfCredit
Namespace Prefix:	gte_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant