Consolidated Statements of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
OPERATING ACTIVITIES
Net income		$ 29,925	$ 42,755	$ 31,183
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of buildings and tenant improvements		25,974	23,453	18,678
Amortization of leasing costs and in-place lease intangibles		11,347	11,875	4,475
Accrued straight-line rental revenue		(1,222)	(1,091)	(1,924)
Amortization of leasing incentives and above or below-market rents		(195)	(85)	738
Accrued straight-line ground rent expense		530	371	290
Bad debt expense		564	203	131
Noncash stock compensation		1,323	1,082	931
Impairment charges		110	355	41
Noncash interest expense		1,274	980	1,006
Noncash loss on extinguishment of debt		50	82	512
Gain on real estate dispositions		(8,087)	(30,533)	(18,394)
Change in the fair value of interest rate derivatives		(1,127)	941	229
Changes in operating assets and liabilities:
Property assets		(2,415)	(2,964)	(2,283)
Property liabilities		2,504	3,761	2,326
Construction assets		17,573	(6,385)	(17,337)
Construction liabilities		(20,110)	15,189	12,664
Net cash provided by operating activities		58,018	59,989	33,266
INVESTING ACTIVITIES
Development of real estate investments		(45,730)	(57,425)	(52,719)
Tenant and building improvements		(12,252)	(6,698)	(5,157)
Acquisitions of real estate investments, net of cash received		(30,026)	(195,645)	(68,445)
Dispositions of real estate investments		12,557	96,670	79,566
Notes receivable issuances		(23,290)	(51,721)	(7,825)
Government development grants		0	0	300
Leasing costs		(2,235)	(2,374)	(2,118)
Leasing incentives		(274)	(236)	(1,563)
Contributions to equity method investments		(1,176)	(8,824)	0
Net cash used for investing activities		(102,426)	(226,253)	(57,961)
FINANCING ACTIVITIES
Proceeds from sales of common stock		96,044	68,475	46,462
Offering costs		(4,663)	(1,453)	(427)
Debt issuances, credit facility and construction loan borrowings		162,585	316,852	214,407
Debt and credit facility repayments, including principal amortization		(160,661)	(186,533)	(206,889)
Debt issuance costs		(2,403)	(1,796)	(1,887)
Redemption of operating partnership units		(5,155)	(58)	(241)
Dividends and distributions		(43,616)	(33,843)	(27,024)
Net cash provided by financing activities		42,131	161,644	24,401
Net decrease in cash, cash equivalents, and restricted cash		(2,277)	(4,620)	(294)
Cash, cash equivalents, and restricted cash, beginning of period		25,193	29,813	30,107
Cash, cash equivalents, and restricted cash, end of period		22,916	25,193	29,813
Supplemental cash flow information:
Cash paid for interest		(16,318)	(15,326)	(12,993)
Cash refunded (paid) for income taxes		(371)	(121)	276
Common shares and OP Units issued for acquisitions	[1]	506	47,278	15,169
Change in accrued capital improvements and development costs		(10,899)	8,183	1,825
Debt principal extinguished in conjunction with real estate sales		5,594	6,400	0
Debt principal assumed in conjunction with real estate acquisitions		$ 0	$ 21,150	$ 13,824

[1] (1) 2017 issuance consists of OP Units contingently issuable upon the satisfaction of certain conditions relating to the Johns Hopkins Village property