Summary of Significant Accounting Policies (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) unit	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) unit measurement	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Restricted cash	$ 1,020		$ 1,020		$ 6,020
Unbilled receivables, current	5,565		5,565		6,755
Billings in excess of cost, current	2,568		2,568		$ 1,730
Provision for losses on contracts	$ 225		$ 225
Number of units with APC technology (in units) | unit	1,000		1,000
Building impairment	$ 0	$ 0	$ 2,965	$ 0
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