Revenue Recognition - Components of Lease Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue from Contract with Customer [Abstract]
Fixed lease revenues	$ 35,903		$ 71,632
Variable lease revenues	17,931		36,698
Lease revenues	$ 53,834	$ 55,906	$ 108,330	$ 111,520