Leases (Summary of Lease Cost) (Details) - USD ($) $ in Thousands		3 Months Ended	6 Months Ended
		Jun. 30, 2019	Jun. 30, 2019
Leases [Abstract]
Operating lease cost		$ 7,998	$ 16,010
Financing lease cost, Amortization of leased assets		12	24
Financing lease, Interest on lease liabilities		19	40
Variable lease cost	[1]	3,333	6,558
Short-term lease cost		218	482
Net lease cost		$ 11,580	$ 23,114

[1] Variable lease costs consist primarily of taxes, insurance, and common area or other maintenance costs for the Company's leased facilities.