Commitments and Contingencies - Outstanding Capital Commitments Associated with Investments in Unconsolidated Affiliates (Detail) - Corporate Joint Venture [Member] - Other Commitments, Engineering, Procurement and Construction Electric Transmission Project [Member] $ in Thousands	Jun. 30, 2016 USD ($)
Other Commitments [Line Items]
Capital commitments, Remainder of 2016	$ 6,852
Capital commitments, 2017	33,199
Capital commitments, 2018	0
Capital commitments, 2019	24,511
Total capital commitments associated with investments in an unconsolidated affiliate related to an EPC electrical transmission project	$ 64,562