Credit Facility (Narrative) (Details) - USD ($)	Dec. 02, 2014	Jun. 30, 2016	Dec. 31, 2015
Line of Credit Facility [Line Items]
Credit facility		$ 304,000,000	$ 304,000,000
Operating Partnership Amended Credit Facility [Member]
Line of Credit Facility [Line Items]
Additional borrowing capacity	$ 575,000,000
Unused borrowing capacity amount		$ 20,900,000
Weighted average interest rate		1.82%
Minimum use percentage	50.00%
Operating Partnership Amended Credit Facility [Member] | Net Worth Greater Than $500 Million [Member]
Line of Credit Facility [Line Items]
Unused capacity commitment fee	0.25%
Unused capacity commitment fee percentage less than 50%	0.15%
Operating Partnership Amended Credit Facility [Member] | Line of Credit Facility, Interest Rate, Option One [Member] | Federal Funds Effective Rate [Member]
Line of Credit Facility [Line Items]
Variable interest rate	0.50%
Operating Partnership Amended Credit Facility [Member] | Line of Credit Facility, Interest Rate, Option One [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Variable interest rate	1.00%
Operating Partnership Amended Credit Facility [Member] | Minimum [Member] | Line of Credit Facility, Interest Rate, Option One [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Variable interest rate	0.35%
Operating Partnership Amended Credit Facility [Member] | Minimum [Member] | Line of Credit Facility, Interest Rate, Option Two [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Variable interest rate	1.35%
Operating Partnership Amended Credit Facility [Member] | Maximum [Member] | Line of Credit Facility, Interest Rate, Option One [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Variable interest rate	1.00%
Operating Partnership Amended Credit Facility [Member] | Maximum [Member] | Line of Credit Facility, Interest Rate, Option Two [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Variable interest rate	2.00%
Operating Partnership Amended Credit Facility [Member] | Swing Line [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 25,000,000
Operating Partnership Amended Credit Facility [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	325,000,000.0
Operating Partnership Amended Credit Facility [Member] | Letter of Credit [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 20,000,000