Lease Obligations (Operating Leases) (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
Operating Leased Assets [Line Items]
Operating lease assets	$ 229,903	$ 0
Operating leases, additions	103,000
Operating leases, variable lease costs	10,400
Operating leases, short-term leases, expense	448,200
Lease Terms in Excess of One Year [Member]
Operating Leased Assets [Line Items]
Operating leases, expense	$ 114,500
Operating leases, rent and related expense		115,000	$ 104,200
Lease Terms in Excess of One Year [Member] | Minimum [Member]
Operating Leased Assets [Line Items]
Operating leases, term of contract (in years)	1 year
Lease Terms of One Year or Less [Member]
Operating Leased Assets [Line Items]
Operating leases, rent and related expense		$ 472,100	$ 461,000
Lease Terms of One Year or Less [Member] | Maximum [Member]
Operating Leased Assets [Line Items]
Operating leases, term of contract (in years)	1 year
ASU 2016-02 [Member]
Operating Leased Assets [Line Items]
Operating lease assets				$ 230,000