Acquisitions - Additional Information (Detail) $ in Thousands			3 Months Ended		9 Months Ended		12 Months Ended
	May. 07, 2015 USD ($)	Apr. 01, 2015 USD ($) mi	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) shares	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Business Acquisition [Line Items]
Business Combination, Separately Recognized Transactions, Additional Disclosures, Acquisition Cost Expensed					$ (514)
Revenues			$ 91,913	$ 91,619	354,676	$ 378,454
Net Income (Loss) Attributable to Parent			5,119	$ 3,180	$ 32,521	$ 25,995	$ 36,092
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life					10 years
Gatherco [Member]
Business Acquisition [Line Items]
Number Of Gathering Stations		16
Number of Pipeline Miles | mi		2,000
Number of Producers Served		300
Number of Customers Served		6,000
Business Combination, Consideration Transferred					$ 57,658
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares					592,970
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned		$ 30,200	30,164		$ 30,164
Payments to Acquire Businesses, Gross		27,500			27,494
Long-term debt		1,696	1,696		1,696
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents		$ 6,800	6,806		6,806
Business Combination Contingent Cash Consideration Payable			15,000		$ 15,000
Period Additional Contingent Cash Consideration Will Be Based On					5 years
Business Combination, Separately Recognized Transactions, Additional Disclosures, Acquisition Cost Expensed					$ (1,300)
Revenues			5,700		11,000
Net Income (Loss) Attributable to Parent			$ 55		$ (133)
Propane Distribution [Member]
Business Acquisition [Line Items]
Number of Customers Served	253
Business Combination, Consideration Transferred	$ 242
Finite-lived Intangible Assets Acquired	$ 186
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life					6 years