Supplemental Information to Statements of Cash Flows - Cash Flow Information (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Supplemental Cash Flow Information [Line Items]
Interest Expense Capitalized in Connection with Development Activity	$ 1,025	$ 742
Supplemental Schedule of Non-Cash Investing and Financing Activities:
Distribution Payable on Common Stock/Operating Partnership Units	14,970		$ 11,949
Exchange of Operating Partnership Units for Common Stock:
Conversion of Units to Common Stock	0	0
Assumption of Liabilities in Connection with the Acquisition of Real Estate	295	183
Accounts Payable Related to Construction in Progress and Additions to Investment in Real Estate	16,863	17,829
Write-off of Fully Depreciated Assets	(20,146)	(19,462)
Noncontrolling Interest
Exchange of Operating Partnership Units for Common Stock:
Conversion of Units to Common Stock	(100)	(1,333)
Common Stock
Exchange of Operating Partnership Units for Common Stock:
Conversion of Units to Common Stock	0	1
Additional Paid-in-Capital
Exchange of Operating Partnership Units for Common Stock:
Conversion of Units to Common Stock	100	1,332
Common Stock
Supplemental Schedule of Non-Cash Investing and Financing Activities:
Distribution Payable on Common Stock/Operating Partnership Units	$ 14,970	$ 11,891