Debt - Additional Information (Detail) (USD $)	6 Months Ended			1 Months Ended						6 Months Ended		6 Months Ended		1 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	May 31, 2014 Unsecured Debt	May 31, 2014 Unsecured Debt Senior Unsecured Note 12-Year Term	May 31, 2014 Unsecured Debt Senior Unsecured Note 10-Year Term	May 31, 2014 Unsecured Debt Variable-Rate Bank Term Debt Due 2017	May 31, 2014 Unsecured Debt Bank Term Debt Due 2017	May 31, 2014 Loans Payable Senior Unsecured Term Loan	Jun. 30, 2014 Fixed Rate Mortgages	Dec. 31, 2013 Fixed Rate Mortgages	Jun. 30, 2014 Mission Bay	Jun. 30, 2014 Hunters Square	May 31, 2014 London Interbank Offered Rate (LIBOR) [Member] Loans Payable Senior Unsecured Term Loan	May 31, 2014 London Interbank Offered Rate (LIBOR) [Member] Loans Payable Senior Unsecured Term Loan Minimum	May 31, 2014 London Interbank Offered Rate (LIBOR) [Member] Loans Payable Senior Unsecured Term Loan Maximum	May 31, 2014 Revolving Credit Facility Unsecured Revolving Credit Facility	May 31, 2014 Interest Rate Swap Loans Payable Senior Unsecured Term Loan
Debt Instrument [Line Items]
Senior unsecured notes				$ 100,000,000	$ 50,000,000	$ 50,000,000			$ 75,000,000
Other long-term debt, term					12 years	10 years			7 years
Additional Borrowing Capacity				50,000,000					75,000,000
Additional Borrowing Capacity Term				3 years
Debt Instrument, Description of Variable Rate Basis														LIBOR
Debt Instrument, Basis Spread on Variable Rate														1.70%	1.25%	2.25%
Fixed rate																		2.90%
Repayments of long-term debt	0						45,000,000	75,000,000
Repayments of Long-term Lines of Credit																	45,000,000
Extinguishment of debt, amount												6,600,000	23,200,000
Mortgage debt interest rate					4.74%	4.65%						5.40%	5.40%
Mortgage debt interest rate, minimum										5.00%
Mortgage debt interest rate, maximum										7.40%
Unamortized premium	2,826,000		3,174,000							2,800,000	3,200,000
Net book value of mortgage on properties										283,300,000
Net repayments on revolving credit facility	27,000,000	37,000,000
Unsecured revolving credit facility	0		27,000,000
Letter of credit, outstanding balance	$ 7,000,000