Summary of Potential Number of Shares Vesting under Restricted Stock (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
at IRR of at least 8.5%
Schedule Of Stock Options [Line Items]
Number of shares vesting at IRR level of at least 8.5%	38,366
Fair value of shares vesting at IRR level of at least 8.5%	$ 1,129
at IRR of at least 10.5%
Schedule Of Stock Options [Line Items]
Number of shares vesting at IRR level of at least 10.5%	76,741
Fair value of shares vesting at IRR level of at least 10.5%	2,259
at IRR of at least 12.5%
Schedule Of Stock Options [Line Items]
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 12.5%	$ 3,389