Consolidated Statements of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
OPERATING ACTIVITIES
Net income		$ 32,258	$ 23,492	$ 29,925
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of buildings and tenant improvements		37,839	30,395	25,974
Amortization of leasing costs, in-place lease intangibles and below market ground rents - operating leases		16,725	9,518	11,347
Accrued straight-line rental revenue		(3,402)	(2,731)	(1,222)
Amortization of leasing incentives and above or below-market rents		(629)	(266)	(195)
Amortization of right-of-use assets - finance leases		377
Accrued straight-line ground rent expense		(16)	214	530
Adjustment for uncollectable accounts		511	419	564
Noncash stock compensation		1,613	1,281	1,323
Impairment charges		252	1,619	110
Noncash interest expense		1,258	1,116	1,274
Interest expense on finance leases		568	0	0
Gain on real estate dispositions		(4,699)	(4,254)	(8,087)
Adjustment for Annapolis Junction purchase option	[1]	(4,489)	4,489	0
Change in the fair value of interest rate derivatives		3,599	951	(1,127)
Equity in income of unconsolidated real estate entities		(273)	(372)	0
Changes in operating assets and liabilities:
Property assets		(2,499)	(3,539)	(2,415)
Property liabilities		3,368	1,720	2,843
Construction assets		(20,356)	7,554	17,573
Construction liabilities		18,671	(15,248)	(20,110)
Interest receivable		(12,947)	(271)	(7,071)
Net cash provided by operating activities		67,729	56,087	51,236
INVESTING ACTIVITIES
Development of real estate investments		(133,445)	(133,791)	(45,730)
Tenant and building improvements		(19,721)	(11,723)	(12,252)
Acquisitions of real estate investments, net of cash received		(138,380)	(57,544)	(30,026)
Dispositions of real estate investments, net of selling costs		32,944	34,673	12,557
Notes receivable issuances		(54,555)	(58,208)	(16,219)
Notes receivable paydowns		22,522	1,165	0
Leasing costs		(3,893)	(4,607)	(2,235)
Leasing incentives		0	(108)	(274)
Contributions to equity method investments		(535)	(10,420)	(1,176)
Net cash used for investing activities		(295,063)	(240,563)	(95,355)
FINANCING ACTIVITIES
Proceeds from issuance of cumulative redeemable perpetual preferred stock, net		61,001	0	0
Proceeds from issuance of common stock, net		96,845	65,244	91,381
Common shares tendered for tax withholding		(369)	(409)	(289)
Debt issuances, credit facility and construction loan borrowings		427,286	349,580	162,585
Debt and credit facility repayments, including principal amortization		(270,851)	(173,855)	(160,661)
Debt issuance costs		(5,546)	(1,457)	(2,403)
Redemption of operating partnership units		0	(2,595)	(5,155)
Dividends on cumulative redeemable perpetual preferred stock		(61,504)	(50,897)	(43,616)
Net cash provided by financing activities		246,862	185,611	41,842
Net increase (decrease) in cash, cash equivalents, and restricted cash		19,528	1,135	(2,277)
Cash, cash equivalents, and restricted cash, beginning of period	[2]	24,051	22,916	25,193
Cash, cash equivalents, and restricted cash, end of period	[2]	43,579	24,051	22,916
Supplemental cash flow information:
Cash paid for interest		28,878	(17,319)	(16,318)
Cash refunded (paid) for income taxes		247	31	(371)
Increase in dividends payable		3,950	1,640	2,160
Common shares and OP units issued for acquisitions	[3]	73,169	1,702	506
(Decrease) increase in accrued capital improvements and development costs		12,666	(18,310)	(10,899)
Operating Partnership units redeemed for common shares		2,756	3,715	0
Debt principal extinguished in conjunction with real estate sales		0	0	5,594
Debt assumed at fair value in conjunction with real estate purchases		101,390	0	0
Debt assumed at fair value in conjunction with real estate purchases		0	0	2,000
Redeemable noncontrolling interest from development		0	0	600
Note receivable extinguished in conjunction with real estate purchase		31,252	0	0
Equity method investment redeemed for real estate acquisition		23,011	0	0
Noncontrolling interest in acquired real estate entity		4,870	0	0
Recognition of operating lease ROU assets	[4]	33,965	0	0
Recognition of operating lease liabilities	[4]	41,631	0	0
Recognition of finance lease ROU assets		24,500	0	0
Recognition of finance lease liabilities		17,871	0	0
De-recognition of operating lease ROU assets - lease termination		440	0	0
De-recognition of operating lease liabilities - lease termination		$ 440	$ 0	$ 0

[1] Borrower paid $5.0 million in 2018 in exchange for the Company's purchase option. This was accounted for as a loan modification fee; interest income was recognized as additional interest income on the note receivable over the one-year remaining term.

[2] The following table sets forth the items from the Company's Consolidated Balance Sheets that are included in cash, cash equivalents, and restricted cash in the consolidated statements of cash flows:   As of December 31,   2019   2018 Cash and cash equivalents $ 39,232
  $ 21,254
Restricted cash ^(a) 4,347
  2,797
Cash, cash equivalents, and restricted cash $ 43,579
  $ 24,051

(a) Restricted cash represents amounts held by lenders for real estate taxes, insurance, and reserves for capital improvements.

[3] 2017 issuance consists of OP Units contingently issuable upon the satisfaction of certain conditions relating to the Johns Hopkins Village property. These OP Units were issued in 2018.

[4] Net of $0.4 million disposal related to the Company's preexisting lease at the Thames Street Wharf property, which was acquired on June 26, 2019.