Summary of Significant Accounting Policies - Construction-in-Progress (Textual) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Construction in Progress [Line Items]
Internal direct construction costs capitalized related to development of properties and land holdings	$ 6,063	$ 6,717	$ 7,291
Development [Member]
Construction in Progress [Line Items]
Internal direct construction costs capitalized related to development of properties and land holdings	4,390	3,182	2,641
Capitalized interest	$ 3,100	$ 10,900	$ 10,200