CONSOLIDATED STATEMENTS OF INCOME (Parenthetical) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
OPERATING COSTS AND EXPENSES
Depreciation included in the cost of petrochemical product sales and processing	$ 4,645us-gaap_CostOfGoodsSoldDepreciation	$ 3,518us-gaap_CostOfGoodsSoldDepreciation	$ 3,053us-gaap_CostOfGoodsSoldDepreciation

The expense recognized in the current period that allocates the cost of a tangible asset over the asset's useful life. This element applies only to an asset used in the production of goods sold.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.2(a))

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

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