Summary of Significant Accounting Policies - Compensation Costs (Including Bonuses and Benefits) Capitalized (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Construction in Progress [Line Items]
Salaries including bonuses and benefits, capitalized during the period	$ 6,063	$ 6,717	$ 7,291
Development [Member]
Construction in Progress [Line Items]
Salaries including bonuses and benefits, capitalized during the period	4,390	3,182	2,641
Redevelopment [Member]
Construction in Progress [Line Items]
Salaries including bonuses and benefits, capitalized during the period	319	144	221
Tenant Improvements [Member]
Construction in Progress [Line Items]
Salaries including bonuses and benefits, capitalized during the period	$ 1,354	$ 3,391	$ 4,429