Accounts Payable and Accrued Liabilities - Schedule of Components of Accounts Payable and Accrued Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Project development activities	$ 1,588	$ 5,142
Payroll and compensation	15,385	25,833
Accrued taxes	2,848	2,764
Professional services (e.g., legal, audit)	4,449	2,806
Other	1,437	2,556
Total accrued liabilities	$ 25,707	$ 39,101