Operating Leases (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Lessee Lease Description [Line Items]
Operating lease right-of-use assets, net	$ 774,837	$ 793,181
Operating lease liabilities	$ 822,751	$ 839,800
Minimum [Member] | Office Space and Office Equipment [Member]
Lessee Lease Description [Line Items]
Operating leases remaining lease term	1 year
Maximum [Member] | Office Space and Office Equipment [Member]
Lessee Lease Description [Line Items]
Operating leases remaining lease term	15 years