Debt Obligations, net (Secured Credit Facility Narrative) (Details)	1 Months Ended				3 Months Ended	7 Months Ended
	Mar. 31, 2017 USD ($) property lease	Jan. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) property	Mar. 31, 2015 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Apr. 14, 2017	Aug. 31, 2016 USD ($)
2017 Secured Financing
Line of Credit Facility [Line Items]
Debt instrument, face amount	$ 227,000,000				$ 227,000,000
Stated interest rates (as a percent)	3.795%				3.795%
Number of properties collateralizing loan | property	12
Number of ground net leases collateralizing loan | lease	7
Number of master lease collateralizing loan | lease	1
Number of properties covered under master lease agreement | property	5
Deferred financing costs	$ 7,400,000				$ 7,400,000
2016 Senior Secured Credit Facility
Line of Credit Facility [Line Items]
Debt instrument, face amount			$ 450,000,000.0			$ 450,000,000.0		$ 500,000,000.0
Percentage of par credit facilities were issued at	99.00%				99.00%
Basis point spread on variable interest rate (as a percent)					1.00%
Multiple of the minimum collateral coverage on outstanding borrowings (at least)	1.25				1.25
Required quarterly principal payment (as a percent)					0.25%
Deferred finance costs, gross						4,500,000
Debt instrument, thirst party fees, amount recognized						6,200,000
Debt issuance fees		$ 800,000
Debt instrument, third party fees, amount capitalized						4,300,000
2016 Senior Secured Credit Facility | Other Expense
Line of Credit Facility [Line Items]
Debt instrument, thirst party fees, amount recognized						$ 1,900,000
2016 Senior Secured Credit Facility | London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Basis point spread on variable interest rate (as a percent)					3.75%	4.50%
2016 Senior Secured Credit Facility | London Interbank Offered Rate (LIBOR) | Minimum
Line of Credit Facility [Line Items]
Basis point spread on variable interest rate (as a percent)					1.00%	1.00%
2016 Senior Secured Credit Facility | London Interbank Offered Rate (LIBOR) | Maximum
Line of Credit Facility [Line Items]
Basis point spread on variable interest rate (as a percent)					2.75%
2015 $250 Million Secured Revolving Credit Facility
Line of Credit Facility [Line Items]
Debt instrument, face amount	$ 250,000,000				$ 250,000,000
Multiple of the minimum collateral coverage on outstanding borrowings (at least)	1.5				1.5
Line of credit facility, maximum borrowing capacity	$ 236,000,000			$ 250,000,000.0	$ 236,000,000
Interest rate during period					3.46%
Converted term loan, term					1 year
2015 $250 Million Secured Revolving Credit Facility | Minimum
Line of Credit Facility [Line Items]
Commitment fee percentage				0.375%
2015 $250 Million Secured Revolving Credit Facility | Maximum
Line of Credit Facility [Line Items]
Commitment fee percentage				0.50%
2015 $250 Million Secured Revolving Credit Facility | London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Basis point spread on variable interest rate (as a percent)					2.75%
2015 $250 Million Secured Revolving Credit Facility | London Interbank Offered Rate (LIBOR) | Minimum
Line of Credit Facility [Line Items]
Basis point spread on variable interest rate (as a percent)					1.00%
2016 Secured Term Loan | Secured Debt
Line of Credit Facility [Line Items]
Debt instrument, face amount			$ 170,000,000.0			$ 170,000,000.0
Number of properties collateralizing loan | property			12
Subsequent Event | Safety, Income nad Growth, Inc.
Line of Credit Facility [Line Items]
Noncontrolling interest (as a percent)							49.00%