Summary of Significant Accounting Policies - Leases - Supplemental Cash Flows (Details) $ in Thousands	3 Months Ended
Mar. 31, 2019 USD ($)
Accounting Policies [Abstract]
Operating cash flows used in operating leases	$ 83,676
Financing cash flows used in financing leases	16,675
Operating lease modifications and reassessments	1,842
New operating leases (including acquisitions)	21,535
Financing lease modifications and reassessments	0
New financing leases	$ 7,523

Amount of cash outflow from operating lease, excluding payments to bring another asset to condition and location necessary for its intended use.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 5
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918643-209977

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (g)(1)
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918686-209980

Name:	us-gaap_OperatingLeasePayments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration