Contract Assets and Contract Liabilities - Narrative (Details) $ in Millions	6 Months Ended
Jun. 30, 2019 USD ($)
Revenue From Contract With Customer [Abstract]
Contract liability billings in excess of costs and estimated earnings on uncompleted contracts	$ 1.0

Contract with customer liability revenue recognized on uncompleted contracts.

No definition available.

Name:	gv_ContractWithCustomerLiabilityRevenueRecognizedOnUncompletedContracts
Namespace Prefix:	gv_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration