Minimum Future Rental Payments under Ground Leases (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Schedule of Operating Leases [Line Items]
Operating leases, future minimum payments payment year 2013	$ 1,915
Operating leases, future minimum payments payment year 2014	1,921
Operating leases, future minimum payments payment year 2015	1,928
Operating leases, future minimum payments payment year 2016	1,935
Operating leases, future minimum payments payment thereafter	13,012
Operating leases, future minimum payments payment	24,064
Operating Leases, Future Minimum Payments Due, Next Twelve Months	$ 3,353