Amount, before allowance for credit loss, of right to consideration in exchange for good or service transferred to customer, when right is conditioned on something other than passage of time.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118944033&loc=SL49130531-203044

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130549-203045

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=118944033&loc=SL49130533-203044

Name:	us-gaap_ContractWithCustomerAssetGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

REVENUES - Disaggregation of Revenues (Details) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2018 USD ($) customer	Dec. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)
Disaggregation of Revenues
Provision for revenue sharing		$ 10.0
Contract balances	$ 44.0	44.0	$ 37.0
Bison
Disaggregation of Revenues
Non-refundable receipt from contract termination		$ 97.0
Number of customers that terminated transportation agreement \| customer	2
Bison \| Tenaska
Disaggregation of Revenues
Non-refundable receipt from contract termination	$ 95.4
Bison \| Another customer
Disaggregation of Revenues
Non-refundable receipt from contract termination	$ 2.0