Significant Accounting Policies - Additional Information (Detail) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) Project	Sep. 30, 2016 Project	Sep. 30, 2017 USD ($) Project Source Method	Sep. 30, 2016 Project	Dec. 31, 2016 USD ($)
Accounting Policies [Abstract]
Number of product revenue sources | Method			2
Unbilled receivables | $	$ 44.1		$ 44.1		$ 56.8
Number of projects | Project	7	4	8	10
Percentage of total revenues	20.00%	12.00%	15.00%	14.00%
Percentage of product revenues	15.00%	14.00%	19.00%	17.00%
Number of service revenue sources | Source			3