Leases - Leases as lessor (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Lease revenue:
Minimum lease revenue	$ 464,005	$ 409,157	$ 367,388
Variable lease revenue (primarily recoveries from customers)	55,853	55,966	46,232
Total lease revenue	$ 519,858	$ 465,123	$ 413,620