Fair Value of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (Significant Unobservable Inputs (Level 3), Cash flow, USD $)	3 Months Ended
	Mar. 31, 2013
Fair Value Measurements [Line Items]
Other assets related to business combinations	830,000	[1]
Contingent consideration related to business combinations	(1,787,000)	[2]
Other Assets Related to Business Combinations
Fair Value Measurements [Line Items]
Unobservable Input, Lease commission	6.00%	[1]
Other Assets Related to Business Combinations | Minimum
Fair Value Measurements [Line Items]
Unobservable Input, Tenant improvement allowance	12	[1]
Unobservable Input, Tenant improvement allowance	2 months	[1]
Other Assets Related to Business Combinations | Maximum
Fair Value Measurements [Line Items]
Unobservable Input, Tenant improvement allowance	35	[1]
Unobservable Input, Tenant improvement allowance	5 months	[1]
Contingent Consideration Related to Business Combinations
Fair Value Measurements [Line Items]
Unobservable Input, Lease commission	6.00%	[2]
Unobservable Input, Tenant improvement allowance	2 months	[2]
Contingent Consideration Related to Business Combinations | Minimum
Fair Value Measurements [Line Items]
Unobservable Input, Tenant improvement allowance	12	[2]
Contingent Consideration Related to Business Combinations | Maximum
Fair Value Measurements [Line Items]
Unobservable Input, Tenant improvement allowance	33	[2]

[1] The significant unobservable inputs used in the fair value measurement of the master lease agreement asset are any estimated tenant improvement allowances, leasing commissions and the construction periods associated with projected new leasing. Significant increases (decreases) in any of these inputs in isolation would result in a significantly higher (lower) fair value measurement. Generally, a change in the assumption used for market lease rates is accompanied by a directionally similar change in the assumption used for tenant improvement allowances and/or leasing commissions.

[2] The significant unobservable inputs used in the fair value measurement of the contingent consideration are any estimated tenant improvement allowances, construction periods, leasing commissions and lease rates. Significant increases (decreases) in any of these inputs in isolation would result in a significantly lower (higher) fair value measurement. Generally, a change in the assumption used for market lease rates is accompanied by a directionally similar change in the assumption used for tenant improvement allowances and/or leasing commissions.