Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue from External Customer [Line Items]
Deferred income	$ 62,319	$ 52,269
Revenues	740,340	657,515	$ 475,212
Tenant Funded Improvements
Revenue from External Customer [Line Items]
Deferred income	31,600	17,800
Tenants Expenses
Revenue from External Customer [Line Items]
Revenues	$ 142,500	$ 122,400	$ 79,800