Summary of Significant Accounting Policies - Additional Information (Details) $ in Millions, $ in Millions	3 Months Ended									12 Months Ended
	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) warehouse	Dec. 31, 2016 USD ($)	Jan. 01, 2019 USD ($)	Dec. 31, 2018 AUD ($)	Dec. 31, 2018 NZD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues		$ 415,817,000	$ 402,010,000	$ 394,667,000	$ 391,141,000	$ 401,721,000	$ 389,501,000	$ 379,451,000	$ 372,914,000	$ 1,603,635,000	$ 1,543,587,000	$ 1,489,999,000
Assets under sale-leaseback agreements		80,300,000				90,500,000				80,300,000	90,500,000	91,600,000
Gain from sale of real estate, net										7,471,000	43,000	11,598,000
Additions										0	3,921,000
Impairment of long-lived assets										747,000	9,473,000	9,820,000
Impairment of inventory											2,100,000
Impairment of investments in partially owned entities										0	6,496,000	0
Cash and cash equivalents		208,078,000				48,873,000				208,078,000	48,873,000	22,834,000
Goodwill impairment										$ 0	0	0
Buildings and improvements | Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, plant, equipment, and leasehold improvements useful lives										5 years
Buildings and improvements | Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, plant, equipment, and leasehold improvements useful lives										40 years
Machinery and equipment | Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, plant, equipment, and leasehold improvements useful lives										3 years
Machinery and equipment | Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, plant, equipment, and leasehold improvements useful lives										20 years
Costs incurred to develop software for internal use and purchased software
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Amortization of property, plant, equipment, and leasehold improvements										$ 5,200,000	5,000,000	4,600,000
Costs incurred to develop software for internal use and purchased software | Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, plant, equipment, and leasehold improvements useful lives										3 years
Costs incurred to develop software for internal use and purchased software | Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, plant, equipment, and leasehold improvements useful lives										10 years
Warehouses
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gain from sale of real estate, net		(900,000)		$ 8,400,000
Operating facilities purchased										$ 13,800,000
Costs to construct for facilities opened			$ 23,400,000
Operating facilities disposed											9,200,000
New facility acquired		13,800,000									$ 31,900,000
Operating Warehouses
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of operating facilities disposed | warehouse											1
Idle Warehouse
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gain from sale of real estate, net		(900,000)
Number of operating facilities disposed | warehouse											2
In-place lease
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Additions										$ 0	$ 3,778,000
Remaining lives of finite-lived intangible assets										4 years 9 months 18 days	5 years 9 months 18 days
In-place lease | Warehouses
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Additions											$ 3,900,000
Customer relationships
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Additions										$ 0	0
Amortization of finite-lived intangible assets										$ 800,000	$ 900,000	1,800,000
Remaining lives of finite-lived intangible assets										9 years 1 month 6 days	10 years
Impairment of finite-lived intangible assets										$ 0	$ 0	0
Customer relationships | Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Useful lives of finite-lived intangible assets										6 years
Customer relationships | Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Useful lives of finite-lived intangible assets										20 years
Below-Market Leases
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Impairment of finite-lived intangible assets										$ 0	0	0
Idle Warehouse | Disposal Group, Held-for-sale, Not Discontinued Operations
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Facility held for sale						2,600,000					2,600,000
Other Income (Expense), Net | Accounting Standards Update 2017-07
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Non-service cost components of retirement benefits											2,800,000	3,500,000
Selling, General and Administrative Expenses | Accounting Standards Update 2017-07
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Non-service cost components of retirement benefits											(2,800,000)	(3,500,000)
Trade Name
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Indefinite lived intangible asset (Trade name)		15,076,000				15,076,000				15,076,000	15,076,000
Scenario, Forecast | Warehouses
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Costs to construct for facilities opened	$ 73,400,000
Scenario, Forecast | Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Finance lease ROU assets													$ 40,800,000
Finance lease obligations													39,200,000
Scenario, Forecast | Accounting Standards Update 2016-02 | Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease obligations													77,600,000
Operating lease ROU assets													74,300,000
Scenario, Forecast | Accounting Standards Update 2016-02 | Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease obligations													80,600,000
Operating lease ROU assets													$ 77,300,000
Australian Subsidiary | Intercompany Loan
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans receivable														$ 153.5
New Zealand Subsidiary | Intercompany Loan
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans receivable															$ 37.5
International
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and cash equivalents		$ 37,300,000				$ 26,800,000				37,300,000	26,800,000
Argentina
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues										$ 11,752,000	$ 18,319,000	$ 19,780,000
Argentina | Operating Income (Loss) | Geographic Concentration Risk
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Concentration risk percentage										3.50%	3.50%	3.50%