Acquisition - Additional information (Detail)			6 Months Ended
	Jun. 30, 2013 USD ($)	Dec. 31, 2012 USD ($)	Jun. 30, 2013 Orbital Gas Systems Limited GBP (£)	Apr. 18, 2013 Orbital Gas Systems Limited USD ($)
Business Acquisition [Line Items]
Business Combination Percentage Equity Interest In Acquiree			100.00%
Business Acquisition Cost Acquired Purchase Price			£ 17,000,000	$ 26,205,500
Common Stock Par Or Stated Value Per Share	$ 0.001	$ 0.001
Business Acquisition of Description obligations of purchase price			5.0% of the purchase price, or £850,000, is held in escrow to and through December 1, 2013.