Restructuring - Narrative (Details) $ in Thousands	3 Months Ended						6 Months Ended	12 Months Ended			24 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2018 USD ($) store	Dec. 31, 2017 USD ($) store	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2017 USD ($) Store
Restructuring Cost and Reserve [Line Items]
Restructuring Expenses	$ 3,400	$ 800	$ 13,500	$ 300	$ 15,500	$ 4,700		$ 17,994	$ 20,218	$ 0
2017 Restructuring Program
Restructuring Cost and Reserve [Line Items]
Restructuring Expenses								$ 3,000
2017 Restructuring Program | Facility Closing
Restructuring Cost and Reserve [Line Items]
Number of store closures | store								15
2017 Restructuring Program | Other Restructuring
Restructuring Cost and Reserve [Line Items]
Restructuring Expenses								$ 1,700
2017 Restructuring Program | Fixed Assets
Restructuring Cost and Reserve [Line Items]
Restructuring Expenses								500
2017 Restructuring Program | Contractual Lease Obligations
Restructuring Cost and Reserve [Line Items]
Restructuring Expenses								800
2016 Restructuring Program
Restructuring Cost and Reserve [Line Items]
Restructuring Expenses								15,000	20,218
2016 Restructuring Program | Facility Closing
Restructuring Cost and Reserve [Line Items]
Number of store closures | Store											123
2016 Restructuring Program | Contractual Lease Obligations
Restructuring Cost and Reserve [Line Items]
Restructuring Expenses								12,600
2016 Restructuring Program | Headcount
Restructuring Cost and Reserve [Line Items]
Restructuring Expenses								1,500
2016 Restructuring Program | Write-down To Fair Value
Restructuring Cost and Reserve [Line Items]
Restructuring Expenses								900
2016 and 2017 Restructuring Program
Restructuring Cost and Reserve [Line Items]
Restructuring Expenses								16,677	15,713		$ 38,200
2016 and 2017 Restructuring Program | Contractual Lease Obligations
Restructuring Cost and Reserve [Line Items]
Restructuring Expenses								$ 13,501	$ 11,830
Forecast | 2017 Restructuring Program
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost remaining							$ 1,500
Forecast | 2017 Restructuring Program | Facility Closing
Restructuring Cost and Reserve [Line Items]
Number of store closures | store							8