Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012 Project	Sep. 30, 2011 Project	Sep. 30, 2012 Project	Sep. 30, 2011 Project	Dec. 31, 2011
Significant Accounting Policies [Line Items]
Unbilled receivables	$ 68.1		$ 68.1		$ 30.5
Number of projects	17	11	19	16
Percentage of total revenue	21.00%	12.80%	19.10%	18.80%
Percentage of product revenues	25.20%	14.80%	22.30%	22.40%