Commitments and Contingencies (Details) employee in Thousands, $ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) employee warehouse agreement	Dec. 31, 1994 USD ($)	Nov. 08, 2018 USD ($)	Nov. 08, 2018 AUD ($)	Dec. 31, 2017 USD ($)
Loss Contingencies [Line Items]
Letter of credit amount outstanding | $					$ 33.8
Number of warehouses | warehouse	155
Land to be purchased under construction commitments			$ 46.6	$ 64.5
Number of employees | employee	11
Number of collective bargaining agreements	69
Number of collective bargaining agreements under negotiation	5
Number of collective bargaining agreements, including agreements under negotiation	74
Number of collective bargaining agreements expiring in 2019	12
Number of warehouses where collective bargaining agreements are expiring in 2019 | warehouse	29
Kansas Breach of Settlement Agreement
Loss Contingencies [Line Items]
Litigation settlement, awarded to other party | $		$ 58.7
Surety Bond
Loss Contingencies [Line Items]
Outstanding surety bond | $	$ 2.7				$ 2.7
Unionized Employees Concentration Risk
Loss Contingencies [Line Items]
Number of warehouses | warehouse	84
Number of Employees | Unionized Employees Concentration Risk
Loss Contingencies [Line Items]
Collective-bargaining arrangement, percentage of participants	56.00%