Restructuring - Narrative (Details) $ in Thousands	3 Months Ended		12 Months Ended			27 Months Ended
	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 store	Dec. 31, 2017 store	Dec. 31, 2016 Store	Mar. 31, 2018 USD ($)
Restructuring Cost and Reserve [Line Items]
Total Restructuring Expenses	$ 906	$ 327
Restructuring Program 2016 and 2017
Restructuring Cost and Reserve [Line Items]
Total Restructuring Expenses						$ 39,200
Restructuring Program 2017
Restructuring Cost and Reserve [Line Items]
Total Restructuring Expenses	400
Expected additional restructuring charges	1,500					$ 1,500
Restructuring Program 2016
Restructuring Cost and Reserve [Line Items]
Total Restructuring Expenses	500
Gain on Sale of Closed Store Properties
Restructuring Cost and Reserve [Line Items]
Total Restructuring Expenses	$ (327)	$ 0
Gain on Sale of Closed Store Properties | Restructuring Program 2017
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, number of store closures | store				15
Gain on Sale of Closed Store Properties | Restructuring Program 2016
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, number of store closures | Store					123
Scenario, Forecast | Gain on Sale of Closed Store Properties | Restructuring Program 2017
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, number of store closures | store			8