Long-Term Debt Letters of Credit (Details) $ in Thousands	Jun. 30, 2019 USD ($)
Bilateral Letter of Credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Interest Rate at Period End	1.75%
Letters of credit outstanding	$ 46,125
Corporate Credit Facility [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Interest Rate at Period End	1.75%
Letters of credit outstanding	$ 27,335
SemCAMS Midstream Credit Facility [Member] [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Interest Rate at Period End	2.25%
Letters of credit outstanding	$ 22,909
SemCAMS Midstream [Member] | Bilateral Letter of Credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Interest Rate at Period End	1.75%
Letters of credit outstanding	$ 3,734