Unsecured Revolving Credit Facility (Narrative) (Details) $ in Thousands		3 Months Ended
	Jan. 07, 2016 item	Mar. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($)
Line Of Credit Facility [Line Items]
Number of extension options | item	2
Outstanding borrowings under the facility | $		$ 90,000	$ 155,000
Unsecured Revolving Credit Facility [Member]
Line Of Credit Facility [Line Items]
Number of lending institutions | item		17
Borrowing capacity under the credit facility | $		$ 600,000
Expandable borrowing capacity under the credit facility | $		$ 1,000,000
Credit facility maturity date		Jul. 01, 2017
Number of extension options | item		2
Credit facility, extension period		6 months
Line of credit facility, bid feature, current borrowing capacity | $		$ 300,000
Terms of the unsecured facility		The terms of the unsecured facility include certain restrictions and covenants which limit, among other things the incurrence of additional indebtedness, the incurrence of liens and the disposition of real estate properties (to the extent that: (i) such property dispositions cause the Company to default on any of the financial ratios of the facility described below, or (ii) the property dispositions are completed while the Company is under an event of default under the facility, unless, under certain circumstances, such disposition is being carried out to cure such default), and which require compliance with financial ratios relating to the maximum leverage ratio (60 percent), the maximum amount of secured indebtedness (40 percent), the minimum amount of fixed charge coverage (1.5 times), the maximum amount of unsecured indebtedness (60 percent), the minimum amount of unencumbered property interest coverage (2.0 times) and certain investment limitations (generally 15 percent of total capitalization).
Terms of dividend restriction		If an event of default has occurred and is continuing, the Corporation will not make any excess distributions except to enable the Corporation to continue to qualify as a REIT under the Code.
Outstanding borrowings under the facility | $		$ 90,000	$ 155,000
Unsecured Revolving Credit Facility 1 [Member]
Line Of Credit Facility [Line Items]
Credit facility extension fee, basis points		0.075%
Unsecured Revolving Credit Facility 2 [Member]
Line Of Credit Facility [Line Items]
Credit facility extension fee, basis points		0.075%
Minimum [Member] | Unsecured Revolving Credit Facility [Member]
Line Of Credit Facility [Line Items]
Fixed charge coverage ratio | item		1.5
Unencumbered property interest coverage | item		2.0
Maximum [Member] | Unsecured Revolving Credit Facility [Member]
Line Of Credit Facility [Line Items]
Leverage ratio		60.00%
Secured indebtedness		40.00%
Unsecured indebtedness		60.00%
Investment limitations as a percentage of total capitalization		15.00%