Summary of Significant Accounting Policies (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) unit measurement	Dec. 31, 2016 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Restricted cash	$ 6,020	$ 6,020
Unbilled receivables, current	3,711	6,755
Billings in excess of cost, current	$ 1,720	$ 1,730
Number of units with APC technology (in units) | unit	1,000
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Contract term (in months)	8 months
Critical operational measurements (in measurements) | measurement	3
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Contract term (in months)	16 months
Critical operational measurements (in measurements) | measurement	4