Segment Information (Entity-Wide Disclosures) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Customer revenues	$ 203,040	$ 237,917
Customer Revenues [Member]
Segment Reporting Information [Line Items]
Customer revenues	203,040	237,917
CAM [Member]
Segment Reporting Information [Line Items]
Non-lease external revenue	800	2,700
Customer revenues	52,376	47,978
CAM [Member] | Customer Revenues [Member]
Segment Reporting Information [Line Items]
Customer revenues	35,887	30,782
All other [Member]
Segment Reporting Information [Line Items]
Customer revenues	19,283	48,868
All other [Member] | Customer Revenues [Member]
Segment Reporting Information [Line Items]
Customer revenues	16,840	36,769
Ground Services [Member] | All other [Member] | Customer Revenues [Member]
Segment Reporting Information [Line Items]
Customer revenues	$ 16,154	$ 36,300