Summary of Potential Number of Shares Vesting under Restricted Stock (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
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%	50,981	51,239	132,144
Fair value of shares vesting at IRR level of at least 8.5%	$ 1,103	$ 991	$ 2,423
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%	101,974	102,488	264,288
Fair value of shares vesting at IRR level of at least 10.5%	2,206	1,983	4,847
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%	152,955	153,727	396,429
Fair value of shares vesting at IRR level of at least 12.5%	$ 3,308	$ 2,975	$ 7,271