Related Party Transactions (Details) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Mar. 09, 2015	Sep. 12, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jul. 01, 2015	Jul. 01, 2014
Related Party Transaction [Line Items]
Total rental income			$ 261,887	$ 246,078	$ 242,757
Investment in WBW CHP LLC, in percentage			47.70%
WBW CHP LLC
Related Party Transaction [Line Items]
Recovered reimbursements of operating expenses of WBW CHP LLC			$ 1,000	$ 1,100	$ 1,100
Common Stock
Related Party Transaction [Line Items]
Common shares issued (in shares)			1,812,451	3,110,067	741,452
AAI Aviation, Inc. | Board of Directors Chairman
Related Party Transaction [Line Items]
Aviation expense			$ 200	$ 100	$ 100
Explorer Insurance Company | Private Placement | Board of Directors Chairman
Related Party Transaction [Line Items]
Common shares issued (in shares)	200,000
Share price (in dollars per share)	$ 40.54
Gross proceeds from issuance of common stock	$ 8,100
ICW Plaza | Board of Directors Chairman
Related Party Transaction [Line Items]
Total rental income			$ 2,200	$ 2,200	$ 2,200
Prepaid Insurance						$ 200	$ 400
Percentage of ownership interests classified as noncontrolling			33.60%
ICW Plaza | Common Stock | Board of Directors Chairman
Related Party Transaction [Line Items]
Percentage of ownership interests classified as noncontrolling			10.10%
ICW Plaza | Member Units | Board of Directors Chairman
Related Party Transaction [Line Items]
Percentage of ownership interests classified as noncontrolling			23.50%
ICW Plaza | Private Placement | Board of Directors Chairman
Related Party Transaction [Line Items]
Common shares issued (in shares)		400,000
Share price (in dollars per share)		$ 33.76
Gross proceeds from issuance of common stock		$ 13,500