Income Taxes - Earliest tax years remaining for federal and major states of operations (Details)	12 Months Ended
Dec. 31, 2017
Federal [Member]
Income Tax Examination [Line Items]
Earliest Open Tax Year	2013
Texas [Member]
Income Tax Examination [Line Items]
Earliest Open Tax Year	2013
Louisiana [Member]
Income Tax Examination [Line Items]
Earliest Open Tax Year	2014
Michigan [Member]
Income Tax Examination [Line Items]
Earliest Open Tax Year	2013

Tax year that remains open to examination under enacted tax laws, in CCYY format.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32718-109319

Name:	us-gaap_OpenTaxYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration