Related Party Transactions (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		12 Months Ended
	Sep. 12, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jul. 01, 2014
Related Party Transaction [Line Items]
Total rental income		$ 246,078	$ 242,757	$ 225,249
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		$ 1,100	1,100	1,000
ICW Plaza | Board of Directors Chairman
Related Party Transaction [Line Items]
Total rental income		$ 2,200	$ 2,200	$ 2,100
Prepaid Insurance					$ 400
Private Placement | ICW Plaza | Board of Directors Chairman
Related Party Transaction [Line Items]
Common shares issued (in shares)	400
Share Price	$ 33.76
Proceeds from Issuance of Common Stock, Gross	$ 13,500