Unaudited Pro forma Financial Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Business Combinations [Abstract]
Revenues	$ 30,768	$ 21,074	$ 82,491	$ 53,182
Net loss attributable to common stockholders	$ (7,627)	$ (4,455)	$ (23,655)	$ (60,016)