Taxes Other Than Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Taxes Other Than Income [Line Items]
Total taxes other than income	$ 14,737	$ 14,140
Property [Member]
Taxes Other Than Income [Line Items]
Total taxes other than income	6,785	6,185
Gross Receipts, Excise And Franchise [Member]
Taxes Other Than Income [Line Items]
Total taxes other than income	2,683	2,519
Payroll [Member]
Taxes Other Than Income [Line Items]
Total taxes other than income	3,124	3,337
Regulatory Assessments [Member]
Taxes Other Than Income [Line Items]
Total taxes other than income	629	672
Pumping Fees [Member]
Taxes Other Than Income [Line Items]
Total taxes other than income	944	918
Other [Member]
Taxes Other Than Income [Line Items]
Total taxes other than income	$ 572	$ 509