Commitments and Contingencies Commitment and Contingencies - Other (Details) - Skanska USA Building Inc. [Member] $ in Millions	9 Months Ended
Sep. 30, 2016 USD ($)
Contractual Obligation	$ 30.0
Payments under contractual obligation	$ 4.9

Amount of contractual obligation, including but not limited to, long-term debt, capital lease obligations, operating lease obligations, purchase obligations, and other commitments.

No definition available.

Name:	us-gaap_ContractualObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant