Costs and Estimated Earnings on Uncompleted Contracts (Narrative) (Details) - customer	9 Months Ended	12 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Costs and Estimated Earnings on Uncompleted Contracts [Abstract]
Costs and estimated earnings in excess of billings on uncompleted contracts, net of billings in excess of costs and estimated earnings, percentage comprised by significant customers	95.10%	87.90%
Number of significant customers	8	8

Costs and estimated earnings in excess of billings on uncompleted contracts net percentage comprised by significant customers.

No definition available.

Name:	sbac_CostsAndEstimatedEarningsInExcessOfBillingsOnUncompletedContractsNetPercentageComprisedBySignificantCustomers
Namespace Prefix:	sbac_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant