Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net income	$ 148,970	$ 204,700	$ 116,144
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization expense	105,394	110,357	108,917
In-place lease adjustment	(1,251)	(901)	118
Tenant improvement reimbursements net of lease incentives	(1,861)	(1,580)	(1,414)
Gain on sale of real estate facilities	(28,235)	(92,373)
Stock compensation	9,245	9,580	(2,532)
Decrease (increase) in receivables and other assets	(989)	792	(247)
Increase (decrease) in accrued and other liabilities	6,799	(2,804)	1,308
Total adjustments	89,102	23,071	106,150
Net cash provided by operating activities	238,072	227,771	222,294
Cash flows from investing activities:
Capital expenditures to real estate facilities	(43,654)	(51,786)	(58,175)
Capital expenditures to land and building held for development	(2,809)	(2,189)	(752)
Investments in unconsolidated joint venture	(5,566)
Acquisition of real estate facilities		(45,021)	(112,955)
Acquisition of land held for development			(990)
Proceeds from sale of real estate facilities	55,160	212,184
Net cash provided by (used in) investing activities	3,131	113,188	(172,872)
Cash flows from financing activities:
Proceeds from the exercise of stock options	5,089	3,054	4,682
Redemption of preferred stock	(75,000)
Distributions paid to preferred shareholders	(59,398)	(60,488)	(59,216)
Distributions paid to common shareholders	(59,377)	(127,838)	(43,972)
Distributions paid to noncontrolling interests - common units	(16,072)	(34,701)	(12,856)
Borrowings on credit facility			115,000
Note receivable from affiliate			(100,000)
Repayment of borrowings on credit facility			(115,000)
Repayment of borrowings on term loan debt			(200,000)
Repayment of note receivable from affiliate			100,000
Principal payments on mortgage notes payable			(47)
Repayment of mortgage notes payable			(18,055)
Net proceeds from the issuance of preferred stock			106,311
Net proceeds from the issuance of common stock			192,329
Net cash used in financing activities	(204,758)	(219,973)	(30,824)
Net increase in cash and cash equivalents	36,445	120,986	18,598
Cash and cash equivalents at the beginning of the period	152,467	31,481	12,883
Cash and cash equivalents at the end of the period	188,912	152,467	31,481
Supplemental disclosures:
Interest paid	14,197	14,200	15,934
Adjustment to noncontrolling interests in underlying operating partnership:
Noncontrolling interests - common units	2,752	2,201	28,031
Paid-in capital	(2,752)	$ (2,201)	(28,031)
Non-cash distributions related to the redemption of preferred stock:
Paid-in capital	2,487
Cumulative distributions	(2,487)
Transfer to investment in unconsolidated joint venture:
Land and building held For development	(21,170)
Investment in unconsolidated joint venture	$ 21,170
Transfer to land and building held for development:
Land			(5,927)
Buildings and improvements			(10,270)
Accumulated depreciation			778
Land and building held for development			$ 15,419