Corporate Restructuring Costs (Narrative) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 9,748	$ 0	$ 28,844	$ 0
Accrual for restructuring costs		19,564		19,564		$ 0
Share-based Compensation Adjustment	[1]	(6,087)	0	339	0
Minimum [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost		44,000		44,000
Maximum [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost		58,000		58,000
Employee Severance and Other Transition Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges		4,100	0	4,593	0
Accrual for restructuring costs		4,254		4,254
Employee Severance and Other Transition Costs [Member] | Minimum [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost		8,000		8,000
Employee Severance and Other Transition Costs [Member] | Maximum [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost		11,000		11,000
Recruitment and Relocation Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	[1]	3,188	0	3,395	0
Accrual for restructuring costs		206		206		0
Recruitment and Relocation Costs [Member] | Minimum [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost		7,000		7,000
Recruitment and Relocation Costs [Member] | Maximum [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost		9,000		9,000
Lease Termination Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	[2]	0	0	15,196	0
Accrual for restructuring costs		14,697		14,697		0
Lease Termination Costs [Member] | Minimum [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost		21,000		21,000
Lease Termination Costs [Member] | Maximum [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost		30,000		30,000
Third-party and Other Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	[1]	2,460	0	5,660	0
Restructuring and related cost, expected cost		6,000		6,000
Accrual for restructuring costs		407		407		$ 0
Non-cash Adjustment[Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	[2]	(1,076)	$ 0	27	$ 0
Share-based Compensation Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost		$ 2,000		$ 2,000

[1] Recorded in general and administrative expenses on the condensed consolidated statement of income.

[2] Recorded in impairment, closure costs, and asset disposals on the condensed consolidated statement of income.