Significant Accounting Policies - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) Project Source Method	Dec. 31, 2017 USD ($) Project
Accounting Policies [Abstract]
Number of product revenue sources | Method	2
Unbilled receivables | $	$ 45.7	$ 41.0
Number of projects | Project	8	7
Percentage of total revenues	11.00%	12.00%
Percentage of product revenues	16.00%	16.00%
Number of service revenue sources | Source	2