Fair Value of Financial Instruments (Other Investments - Pacer) (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Other investment, proceeds									$ 5,415	$ 23,801	$ 1,125
Other current assets	$ 47,330				$ 35,763				47,330	35,763
Revenue	1,917,600	$ 1,977,200	$ 1,617,800	$ 1,396,800	1,602,900	$ 1,955,800	$ 1,890,200	$ 1,158,200	6,909,417	6,606,978	5,134,703
Pacer [Member] | Investment [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Other investment, changes in expected recovery estimates, (expense) income									(900)	(400)	3,600
Other investment, proceeds									5,400	22,500
Other current assets	$ 2,900				$ 9,600				$ 2,900	$ 9,600
Revenue											$ 600