Summary of Potential Number of Shares Vesting under Restricted Stock Unit Awards (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Schedule of Restricted Stock Unit [Line Items]
Number of shares vesting at IRR level of at least 8.5%	38,366
Number of shares vesting at IRR level of at least 10.5%	76,741
Number of shares vesting at IRR level of at least 12.5%	115,107
Fair value of shares vesting at IRR level of at least 8.5%	$ 1,129
Fair value of shares vesting at IRR level of at least 10.5%	2,259
Fair value of shares vesting at IRR level of at least 12.5%	$ 3,389