Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income	$ 179,316	$ 144,984	$ 148,970
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	94,270	99,486	105,394
Tenant improvement reimbursements, net of lease incentives	(2,183)	(1,666)	(1,861)
Equity in loss of unconsolidated joint venture	805
Gain on sale of real estate facilities	(1,209)		(28,235)
Gain on sale of development rights	(6,365)
Stock compensation	4,777	10,913	9,245
Amortization of financing costs	475	523	706
Other, net	1,728	(3,733)	4,620
Total adjustments	92,298	105,523	89,869
Net cash provided by operating activities	271,614	250,507	238,839
Cash flows from investing activities:
Capital expenditures to real estate facilities	(50,219)	(31,877)	(43,654)
Capital expenditures to land and building held for development	(1,549)	(49)	(2,809)
Investment in and advances to unconsolidated joint venture	(34,513)	(40,454)	(5,566)
Acquisition of real estate facilities		(12,628)
Proceeds from sale of real estate facilities	2,144		55,160
Proceeds from sale of development rights	4,900
Net cash (used in) provided by investing activities	(79,237)	(85,008)	3,131
Cash flows from financing activities:
Proceeds from the exercise of stock options	4,218	3,888	5,089
Net proceeds from the issuance of preferred stock	415,779	183,316
Redemption of preferred stock	(450,000)		(75,000)
Cash paid for taxes in lieu of shares upon vesting of restricted stock units	(3,865)	(1,940)	(767)
Cash paid to restricted stock unit holders	(761)	(569)
Distributions paid to preferred shareholders	(52,180)	(57,276)	(59,398)
Distributions paid to common shareholders	(92,531)	(81,285)	(59,377)
Distributions paid to noncontrolling interests	(24,838)	(21,916)	(16,072)
Borrowings on credit facility	250,000	116,000
Repayment of borrowings on credit facility	(250,000)	(116,000)
Repayment of mortgage note payable		(250,000)
Payment of financing costs	(858)
Net cash used in financing activities	(205,036)	(225,782)	(205,525)
Net increase (decrease) in cash and cash equivalents	(12,659)	(60,283)	36,445
Cash and cash equivalents at the beginning of the period	128,629	188,912	152,467
Cash and cash equivalents at the end of the period	115,970	128,629	188,912
Supplemental disclosures:
Interest paid	1,188	7,395	14,197
Adjustment to noncontrolling interests in OP
Noncontrolling interests	(271)	2,313	2,752
Paid-in capital	271	(2,313)	(2,752)
Preferred Redemption Allocation
Paid-in capital	10,978	7,312	2,487
Accumulated earnings (deficit)	(10,978)	(7,312)	(2,487)
Preferred stock called for redemption:
Preferred stock called for redemption and reclassified to liabilities	130,000	230,000
Preferred stock called for redemption and reclassified from equity	(130,000)	(230,000)
Accrued Preferred Stock Distributions
Accrued and other liabilities	693
Accumulated earnings (deficit)	$ (693)
Transfer to land and building held for development:
Land		(9,676)
Buildings and improvements		(19,092)
Accumulated depreciation		7,870
Land and building held for development		20,898
Cumulative effect of a change in accounting principle (Note 11):
Paid-in capital		807
Accumulated earnings (deficit)		$ (807)
Transfer to investment in and advances to unconsolidated joint venture:
Land and building held for development			(21,170)
Investment in and advances to unconsolidated joint venture			$ 21,170