Significant Accounting Policies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014 Segment	Dec. 31, 2013	Dec. 31, 2012
Accounting Policies [Line Items]
Business segments	4
Interest capitalized	$ 3,100,000	$ 600,000
Indirect project costs	2,400,000	1,600,000	400,000
Capitalized preacquisition development costs	4,550,000	2,036,000
Accounts receivable, net	20,548,000	18,272,000
Stock-based compensation expense	917,000	1,249,000
Capitalized stock-based compensation	400,000
Percentage of taxable income for distributions to stockholders	90.00%
Johns Hopkins Village [Member]
Accounting Policies [Line Items]
Capitalized preacquisition development costs	2,100,000	500,000
Accrued Straight-line Rental Revenue [Member]
Accounting Policies [Line Items]
Accounts receivable, net	$ 19,400,000	$ 17,500,000