CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 56,859	$ 40,052	$ 31,612
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	95,702	80,722	65,785
Amortization of above/below market leases	(520)	(556)	(823)
Amortization of deferred financing costs	1,246	1,897	1,739
Gain on real estate disposal	(36)	(1,208)
Share-based compensation	7,114	6,125	6,770
Bad debt expense	201	648	244
Changes in operating assets and liabilities:
Accounts receivable	(2,146)	(599)	(682)
Deferred rent receivable	(7,799)	(4,245)	(2,248)
Deferred leasing costs	(17,555)	(21,390)	(6,852)
Other assets	(5,535)	(4,459)	(7,157)
Accounts payable and accrued expenses	6,532	(4,160)	3,756
Unearned revenue, prepaid rent and other liabilities	9,561	7,350	262
Deferred rent payable	(1,051)	(661)	5,317
Net cash provided by operating activities	142,573	99,516	97,723
CASH FLOWS FROM INVESTING ACTIVITIES
Tenant improvements	(7,736)	(5,893)	(7,128)
Real estate improvements	(122,196)	(100,299)	(185,452)
Acquisition of NY2			(21,889)
Proceeds from real estate disposal	2,399	(946)
Net cash used in investing activities	(127,533)	(106,192)	(214,469)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from exercise of stock options	1,393	2,354	925
Offering costs		(147)	(27)
Proceeds from revolving credit facility	87,000	88,250	174,250
Payments on revolving credit facility	(163,250)	(44,000)
Proceeds from senior unsecured term loan	150,000	100,000
Repayments of mortgage loans payable		(58,250)	(1,500)
Payments of loan fees and costs	(2,315)	(1,000)	(2,621)
Payments to net settle equity awards	(4,256)	(1,410)
Dividends and distributions	(87,420)	(73,772)	(57,098)
Net cash provided by (used in) financing activities	(18,848)	12,025	113,929
Net change in cash and cash equivalents	(3,808)	5,349	(2,817)
Cash and cash equivalents, beginning of period	10,662	5,313	8,130
Cash and cash equivalents, end of period	6,854	10,662	5,313
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION
Cash paid for interest, net of capitalized amounts	6,219	4,072	2,044
NON-CASH INVESTING AND FINANCING ACTIVITY
Construction costs payable capitalized to real estate	37,033	16,142	19,821
Accrual of dividends and distributions	$ 28,104	$ 22,355	$ 18,804