Commitments and Contingencies (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) $ / square_foot	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Loss Contingencies [Line Items]
Rental expense	$ 73,800	$ 64,300	$ 84,600
Consolidation of leased facilities	14,218	9,718	28,857
Sublease income	200	$ 200	$ 200
Liability for loss on lease obligation	43,400
Purchase obligations anticipated for 2018	5,300
Contingent obligations to purchase inventory	16,600
Other purchase commitments, due in fiscal 2019	25,000
Other purchase commitments, due in fiscal 2020	25,000
One Office Location
Loss Contingencies [Line Items]
Liability for loss on lease obligation	$ 42,300
Operating lease, change in price per square foot (dollars per square foot) | $ / square_foot	0.50
Operating lease, change in price per square foot, percent	20.00%
Impact on liabilities for loss on lease obligation if price per square foot assumtion changed by $0.50	$ 4,900