Financing Obligations - Narrative (Details) $ in Millions		3 Months Ended	12 Months Ended
Oct. 10, 2017 USD ($) property period	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Leases [Abstract]
Sale leaseback transaction, number of properties \| property	42
Sale leaseback transaction, gross proceeds \| $	$ 119.5	$ 4.7	$ 0.0	$ 6.4
Sale leaseback transaction, lease term (in years)	20 years
Sale leaseback transaction, number of additional periods \| period	5
Sale leaseback transaction, length of each additional period (in years)	5 years

Amount of cash inflow before closing and debt issuance costs received by a seller-lessee in a sale-leaseback recognized in financing activities.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 40
-Section 55
-Paragraph 50
-URI http://asc.fasb.org/extlink&oid=82846721&loc=d3e51831-112757

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 40
-Section 55
-Paragraph 52
-URI http://asc.fasb.org/extlink&oid=82846721&loc=d3e51843-112757

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 40
-Section 55
-Paragraph 51
-URI http://asc.fasb.org/extlink&oid=82846721&loc=d3e51840-112757

Name:	us-gaap_SaleLeasebackTransactionGrossProceedsFinancingActivities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration