Summary of Changes in Fair Value of Level Three Forward Purchase Contracts (Detail) (Fair Value, Inputs, Level 3, USD $)	12 Months Ended
	Dec. 31, 2012
Fair Value, Instruments Classified in Shareholders' Equity Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance
Issuance	29,317
Adjustments to fair value included in other income (expense)	(1,237)
Transfers to additional paid-in-capital	(28,080)
Ending Balance
The February 2012 Forward Purchase Contract
Fair Value, Instruments Classified in Shareholders' Equity Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance
Issuance	1,080
Adjustments to fair value included in other income (expense)	12,011
Transfers to additional paid-in-capital	(13,091)
Ending Balance
The October 2012 Forward Purchase Contract
Fair Value, Instruments Classified in Shareholders' Equity Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance
Issuance	28,237
Adjustments to fair value included in other income (expense)	(13,248)
Transfers to additional paid-in-capital	(14,989)
Ending Balance