Equity-Based Compensation - Share Option Activity (Detail) (USD $)	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Jun. 30, 2013	Dec. 31, 2012
Share option activity
Options Outstanding, Beginning balance		5,275,000
Options Outstanding, Granted
Options Outstanding, Exercised	1,900,000	(1,875,000)
Options Outstanding, Forfeited
Options Outstanding, Ending balance	3,400,000	3,400,000	5,275,000
Options Outstanding, Exercisable Number	274,997	274,997
Weighted Average Exercise Price, Beginning balance		$ 8.44
Weighted Average Exercise Price, Granted
Weighted Average Exercise Price, Exercised		$ 8.00
Weighted Average Exercise Price, Forfeited
Weighted Average Exercise Price, Ending balance	$ 8.68	$ 8.68	$ 8.44
Weighted Average Exercise Price, Exercisable price per share		$ 10.16
Aggregate Fair Value, Beginning balance		$ 29,020
Aggregate Fair Value, Granted
Aggregate Fair Value, Exercised		(10,538)
Aggregate Fair Value, Forfeited
Aggregate Fair Value, Ending balance	18,482	18,482	29,020
Aggregate Fair Value, Exercisable price	$ 1,464	$ 1,464
Weighted Average Remaining Contractual Term		7 years 6 months 22 days	8 years 4 days
Weighted Average Remaining Contractual Term, Exercisable		7 years 9 months