Real Estate Investments - Narrative (Details) (USD $)	3 Months Ended		9 Months Ended				3 Months Ended		9 Months Ended			1 Months Ended			0 Months Ended	3 Months Ended		9 Months Ended	0 Months Ended		3 Months Ended	0 Months Ended		3 Months Ended	12 Months Ended	0 Months Ended			9 Months Ended	3 Months Ended	9 Months Ended	0 Months Ended			0 Months Ended		0 Months Ended		0 Months Ended		0 Months Ended		0 Months Ended		1 Months Ended			0 Months Ended		1 Months Ended	3 Months Ended
	Sep. 30, 2014 sqft property	Sep. 30, 2013	Sep. 30, 2014 sqft property	Sep. 30, 2013	Dec. 31, 2013 Property	Dec. 31, 2013 property	Sep. 30, 2014 Discontinued Operations [Member]	Sep. 30, 2013 Discontinued Operations [Member]	Sep. 30, 2014 Discontinued Operations [Member]	Sep. 30, 2013 Discontinued Operations [Member]	Dec. 31, 2013 Discontinued Operations [Member]	Apr. 30, 2014 TEXAS	Sep. 30, 2014 TEXAS	Sep. 30, 2014 PENNSYLVANIA Potential Disposition [Member]	Mar. 28, 2014 Other Mortgage Loans [Member] Other Property [Member] IOWA	Mar. 31, 2014 Other Mortgage Loans [Member] Other Property [Member] IOWA	Mar. 28, 2014 Other Mortgage Loans [Member] Other Property [Member] IOWA	Sep. 30, 2014 Real Estate Dispositions [Member] sqft	Apr. 23, 2014 Real Estate Dispositions [Member] TEXAS Medical Building Disposed April 23 2014 [Member] sqft		Mar. 31, 2014 Real Estate Dispositions [Member] TEXAS Medical Building Disposed April 23 2014 [Member]	Apr. 11, 2014 Real Estate Dispositions [Member] FLORIDA Medical Building Disposed April 11 2014 [Member] sqft		Mar. 31, 2014 Real Estate Dispositions [Member] FLORIDA Medical Building Disposed April 11 2014 [Member]	Dec. 31, 2013 Real Estate Dispositions [Member] FLORIDA Medical Building Disposed April 11 2014 [Member]	Sep. 12, 2014 Real Estate Dispositions [Member] NEVADA Medical Building Disposed September 12, 2014 [Member]	Sep. 30, 2014 Real Estate Dispositions [Member] NEVADA Medical Building Disposed September 12, 2014 [Member]	Sep. 12, 2014 Real Estate Dispositions [Member] NEVADA Medical Building Disposed September 12, 2014 [Member] sqft	Sep. 30, 2014 Mortgage Note Repayments [Member] mortgage_note_receivable	Sep. 30, 2014 Transferred to Held For Sale [Member] Discontinued Operations [Member]	Sep. 30, 2014 Real Estate Acquisitions [Member] sqft	May 22, 2014 Real Estate Acquisitions [Member] OKLAHOMA	Sep. 30, 2014 Real Estate Acquisitions [Member] OKLAHOMA	May 22, 2014 Real Estate Acquisitions [Member] OKLAHOMA sqft	Jun. 06, 2014 Real Estate Acquisitions [Member] NORTH CAROLINA	Jun. 06, 2014 Real Estate Acquisitions [Member] NORTH CAROLINA sqft	Jun. 04, 2014 Real Estate Acquisitions [Member] TEXAS	Jun. 04, 2014 Real Estate Acquisitions [Member] TEXAS sqft	Sep. 16, 2014 Real Estate Acquisitions [Member] FLORIDA	Sep. 16, 2014 Real Estate Acquisitions [Member] FLORIDA sqft	Mar. 28, 2014 Real Estate Acquisitions [Member] IOWA	Mar. 28, 2014 Real Estate Acquisitions [Member] IOWA sqft	Jul. 28, 2014 Real Estate Acquisitions [Member] MINNESOTA		Jul. 31, 2014 Real Estate Acquisitions [Member] MINNESOTA	Jul. 28, 2014 Real Estate Acquisitions [Member] MINNESOTA sqft	Jun. 04, 2014 Medical Office Building [Member] TEXAS	Jun. 04, 2014 Real Estate Assets [Member] Medical Office Building [Member] TEXAS	Jun. 04, 2014 Real Estate Assets [Member] Medical Office Building [Member] TEXAS	Oct. 31, 2014 Subsequent Event [Member] Real Estate Acquisitions [Member] OKLAHOMA sqft	Mar. 31, 2015 Scenario, Forecast [Member] PENNSYLVANIA Potential Disposition [Member]
Acquisitions and Dispositions [Line Items]
Square footage																															544,433			200,000		35,292		48,048		47,962		152,655				60,476				68,860
Purchase price																															$ 128,300,000	$ 85,400,000			$ 6,500,000		$ 8,700,000		$ 7,900,000		$ 0		$ 19,800,000	[1]						$ 17,400,000
Cash consideration																															35,800,000	4,200,000			6,500,000		8,800,000		7,900,000				8,400,000	[1]						10,600,000
Debt assumed																																														11,400,000				6,800,000
Mortgage contractual interest rate																																																		6.10%
Fair value adjustment premium																																											1,200,000		1,200,000
Weighted average contractual interest rate																																														6.67%
Percentage of medical office building leased																																		100.00%		100.00%				89.00%						100.00%				96.70%
Face amount of mortgages																	40,000,000																	81,200,000
Additional funded amount																																4,000,000
Anticipated amount of investment																																	1,800,000
Real estate properties, cost	3,241,540,000		3,241,540,000			3,067,187,000	23,920,000		23,920,000		16,978,000																						91,200,000
Limited liability company, ownership percentage																																															56.90%
Cash consideration																																																	8,800,000
Closing costs																																																100,000
Stated interest rate, percent															7.70%
Incremental Interest Rate for Default																3.00%
Exit fee																1,500,000
Area Covered Under Real Estate Investment Sold in Measurement Units	141,999		141,999															141,999	58,365	[2]		52,608	[2]					31,026
Real estate investment disposed of during period	10,700,000		10,700,000															10,700,000	4,100,000	[2]		1,700,000	[2]					4,900,000
Net investment in potential disposition	2,548,023,000		2,548,023,000			2,435,078,000	11,019,000		11,019,000		6,767,000			7,700,000
Disposition Sales Price	8,500,000		8,500,000															8,500,000	4,400,000	[2]		1,800,000	[2]					2,300,000																							15,000,000
Gain/(Impairment)			(2,800,000)															(2,800,000)								(2,800,000)																									7,300,000
Net cash proceeds			11,000,000															6,100,000	4,200,000	[2]		1,700,000	[2]			200,000			4,900,000
Seller Financed Mortgage Notes Receivable	(3,000,000)		(3,000,000)															1,900,000									1,900,000	1,900,000	(4,900,000)
Closing costs on disposition	500,000		500,000															500,000	200,000	[2]		100,000	[2]					200,000
Impairment charges																					2,600,000			900,000	2,400,000	2,800,000
Number of Mortgage Notes Receivables Repaid																													2
Noncontrolling interest, ownership percentage by parent												40.00%
Purchase of noncontrolling interests												8,200,000
Noncontrolling interest	0		0			1,809,000							1,600,000
Impairments	$ 4,505,000	$ 6,259,000	$ 11,034,000	$ 9,889,000			$ 4,505,000	$ 6,259,000	$ 11,034,000	$ 9,889,000																				$ 1,800,000
Number of properties held for sale	4		4		3	3

[1] The mortgage note payable assumed in the acquisition does not reflect the fair value adjustment of $1.2 million recorded by the Company upon acquisition (included in Other).

[2] Previously included in assets held for sale.