Leases - Leases as lessor (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Lease revenue:
Minimum lease revenue	$ 113,147	$ 101,947	$ 220,632	$ 200,543
Variable lease revenue (primarily recoveries from customers)	12,849	13,030	25,445	23,823
Total lease revenue	$ 125,996	$ 114,977	$ 246,077	$ 224,366