Condensed Consolidating Financial Statements (Narrative) (Details)	3 Months Ended
Mar. 31, 2018
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Subsidiaries, ownership percentage	100.00%

The number of units or percentage investment held in the subsidiary by the limited liability company or limited partnership.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611443-123010

Name:	us-gaap_SubsidiaryOfLimitedLiabilityCompanyOrLimitedPartnershipOwnershipInterest
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration