Guarantor and Non-Guarantor Financial Information - Condensed Consolidated Statements of Cash Flows (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Condensed Financial Statements, Captions [Line Items]
Net Cash Provided by Operating Activities	$ 102,744	$ 96,487
Cash Flows from Investing Activities:
Investment in real estate assets and real estate related intangibles, net of accruals	(64,422)	(107,772)
Intercompany note receivable	0	0
Redemption of noncontrolling interest in unconsolidated variable interest entity	0	(4,000)
Net sales proceeds from wholly-owned properties	201,690	87,925
Deferred lease costs paid	(6,266)	(10,678)
Net cash provided by/(used in) investing activities	131,002	(34,525)
Cash Flows from Financing Activities:
Debt issuance costs paid	(138)	(830)
Proceeds from debt	211,000	1,054,857
Repayments of debt	(357,597)	(1,012,576)
Intercompany note payable	0
Costs of issuance of common stock	(42)	(326)
Shares withheld to pay tax obligations related to employee stock compensation	(2,283)	(1,654)
Repurchases of common stock as part of announced plan	(7,943)	(39,914)
(Distributions to)/repayments from affiliates	0	0
Dividends paid and discount on dividend reinvestments	(61,075)	(64,828)
Net cash used in financing activities	(218,078)	(65,271)
Net increase/(decrease) in cash and cash equivalents	15,668	(3,309)
Cash and cash equivalents, beginning of period	5,441	12,306
Cash and cash equivalents, end of period	21,109	8,997
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net Cash Provided by Operating Activities	19,628	17,187
Cash Flows from Investing Activities:
Investment in real estate assets and real estate related intangibles, net of accruals	0	0
Intercompany note receivable	(9,600)	(72,000)
Redemption of noncontrolling interest in unconsolidated variable interest entity		0
Net sales proceeds from wholly-owned properties	0	0
Deferred lease costs paid	0	0
Net cash provided by/(used in) investing activities	(9,600)	(72,000)
Cash Flows from Financing Activities:
Debt issuance costs paid	0	0
Proceeds from debt	0	0
Repayments of debt	0	72,000
Intercompany note payable	9,600
Costs of issuance of common stock	0	0
Shares withheld to pay tax obligations related to employee stock compensation	0	0
Repurchases of common stock as part of announced plan	0	0
(Distributions to)/repayments from affiliates	(19,628)	(17,187)
Dividends paid and discount on dividend reinvestments	0	0
Net cash used in financing activities	(10,028)	54,813
Net increase/(decrease) in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	0	0
Issuer [Member]
Condensed Financial Statements, Captions [Line Items]
Net Cash Provided by Operating Activities	(14,105)	(15,322)
Cash Flows from Investing Activities:
Investment in real estate assets and real estate related intangibles, net of accruals	(13,062)	(10,269)
Intercompany note receivable	0	72,000
Redemption of noncontrolling interest in unconsolidated variable interest entity		0
Net sales proceeds from wholly-owned properties	108,550	87,925
Deferred lease costs paid	(1,712)	(2,027)
Net cash provided by/(used in) investing activities	93,776	147,629
Cash Flows from Financing Activities:
Debt issuance costs paid	(138)	(423)
Proceeds from debt	211,000	895,578
Repayments of debt	(232,000)	(907,000)
Intercompany note payable	(9,600)
Costs of issuance of common stock	0	0
Shares withheld to pay tax obligations related to employee stock compensation	0	0
Repurchases of common stock as part of announced plan	0	0
(Distributions to)/repayments from affiliates	(34,837)	(122,441)
Dividends paid and discount on dividend reinvestments	0	0
Net cash used in financing activities	(65,575)	(134,286)
Net increase/(decrease) in cash and cash equivalents	14,096	(1,979)
Cash and cash equivalents, beginning of period	2,174	8,143
Cash and cash equivalents, end of period	16,270	6,164
Guarantor [Member]
Condensed Financial Statements, Captions [Line Items]
Net Cash Provided by Operating Activities	3,075	2,869
Cash Flows from Investing Activities:
Investment in real estate assets and real estate related intangibles, net of accruals	0	0
Intercompany note receivable	0	0
Redemption of noncontrolling interest in unconsolidated variable interest entity		0
Net sales proceeds from wholly-owned properties	0	0
Deferred lease costs paid	0	0
Net cash provided by/(used in) investing activities	0	0
Cash Flows from Financing Activities:
Debt issuance costs paid	0	0
Proceeds from debt	0	0
Repayments of debt	0	0
Intercompany note payable	0
Costs of issuance of common stock	(42)	(326)
Shares withheld to pay tax obligations related to employee stock compensation	(2,283)	(1,654)
Repurchases of common stock as part of announced plan	(7,943)	(39,914)
(Distributions to)/repayments from affiliates	68,259	102,205
Dividends paid and discount on dividend reinvestments	(61,066)	(64,820)
Net cash used in financing activities	(3,075)	(4,509)
Net increase/(decrease) in cash and cash equivalents	0	(1,640)
Cash and cash equivalents, beginning of period	150	1,790
Cash and cash equivalents, end of period	150	150
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net Cash Provided by Operating Activities	94,146	91,753
Cash Flows from Investing Activities:
Investment in real estate assets and real estate related intangibles, net of accruals	(51,360)	(97,503)
Intercompany note receivable	9,600	0
Redemption of noncontrolling interest in unconsolidated variable interest entity		(4,000)
Net sales proceeds from wholly-owned properties	93,140	0
Deferred lease costs paid	(4,554)	(8,651)
Net cash provided by/(used in) investing activities	46,826	(110,154)
Cash Flows from Financing Activities:
Debt issuance costs paid	0	(407)
Proceeds from debt	0	159,279
Repayments of debt	(125,597)	(177,576)
Intercompany note payable	0
Costs of issuance of common stock	0	0
Shares withheld to pay tax obligations related to employee stock compensation	0	0
Repurchases of common stock as part of announced plan	0	0
(Distributions to)/repayments from affiliates	(13,794)	37,423
Dividends paid and discount on dividend reinvestments	(9)	(8)
Net cash used in financing activities	(139,400)	18,711
Net increase/(decrease) in cash and cash equivalents	1,572	310
Cash and cash equivalents, beginning of period	3,117	2,373
Cash and cash equivalents, end of period	$ 4,689	$ 2,683