Investments - Narrative (Details) $ in Thousands						1 Months Ended	3 Months Ended			9 Months Ended		12 Months Ended
	Apr. 27, 2016 USD ($)	Sep. 09, 2014 USD ($) ft²	Jun. 20, 2014 USD ($)	Apr. 12, 2013	Apr. 10, 2013 USD ($) building	Apr. 30, 2016 USD ($)	Sep. 30, 2016 USD ($)	Mar. 31, 2016	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)	Jan. 31, 2016 USD ($)	Jun. 16, 2014 ft²
Schedule of Equity Method Investments [Line Items]
Issuance of limited partnership units										$ 11,941		$ 7,282
Total principal							$ 1,462,975			1,462,975		1,485,516
Payment to unaffiliated third party investors										3,022		3,150
Gain on acquisition of unconsolidated entity							0		$ 0	666	$ 0
Equity in other comprehensive loss of unconsolidated joint venture							327		$ (539)	(456)	$ (670)
Noncontrolling interest redemption value													$ 18,100
Mortgages
Schedule of Equity Method Investments [Line Items]
Total principal							365,566			365,566		363,863
Non- controlling Interests
Schedule of Equity Method Investments [Line Items]
Issuance of limited partnership units						$ 11,900				11,941		7,282
Payment to unaffiliated third party investors										3,022		3,150
HealthSpring | Mortgages
Schedule of Equity Method Investments [Line Items]
Total principal							$ 22,260			$ 22,260		$ 0
HealthSpring
Schedule of Equity Method Investments [Line Items]
Property interest acquired (percent)	90.00%
Payments to acquire property	$ 37,200
HealthSpring DST
Schedule of Equity Method Investments [Line Items]
Payments to acquire buildings					$ 36,400
Equity method investment, liabilities and equity	27,500				39,600
Equity method investment, liabilities					23,600
Equity method investment, equity					$ 16,000
Operating leases, term of contract					9 years
Equity method investment, ownership (percent)				10.00%
Offering expense discount				10.00%
Payment to unaffiliated third party investors	5,000
HealthSpring DST | Non- controlling Interests
Schedule of Equity Method Investments [Line Items]
Issuance of limited partnership units						$ 11,900
HealthSpring DST | HealthSpring | Mortgages
Schedule of Equity Method Investments [Line Items]
Total principal	$ 22,400
HealthSpring DST | HealthSpring
Schedule of Equity Method Investments [Line Items]
Number of buildings acquired | building					2
Property interest acquired (percent)	90.00%							10.00%
Payments to acquire property	$ 41,300
Percent of investors electing exchange of company units (percent)	70.00%
Percent of investors electing cash (percent)	30.00%
Gain on acquisition of unconsolidated entity	$ 700
Digital Realty Joint Venture
Schedule of Equity Method Investments [Line Items]
Equity method investment, liabilities		$ 102,000
Operating leases, term of contract		6 years
Equity method investment, ownership (percent)		80.00%
Payments to acquire interest in equity method investment		$ 68,400
Equity method investment, property		$ 187,500
Area of real estate property (in sqft) | ft²		132,300
WR Griffin Patterson, LLC
Schedule of Equity Method Investments [Line Items]
Operating leases, term of contract			15 years
Area of real estate property (in sqft) | ft²														1,500,000
Land acquisition - real estate development			$ 15,200