Acquisitions - Additional Information (Detail) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
	Apr. 01, 2015 USD ($) mi	Sep. 30, 2016 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) $ / shares	Sep. 30, 2016 USD ($) $ / shares	Sep. 30, 2015 USD ($) $ / shares	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Business Acquisition [Line Items]
Transaction costs						$ 514	$ 786
Revenues		$ 108,348	$ 91,913	$ 356,986	$ 354,676
Net income		$ 4,416	$ 5,119	$ 32,812	$ 32,521	41,140
Diluted (in dollars per share) | $ / shares		$ 0.29	$ 0.33	$ 2.14	$ 2.16
Goodwill		$ 15,070		$ 15,070		14,548
Gatherco [Member]
Business Acquisition [Line Items]
Number of pipeline miles | mi	2,500
Number of counties served	40
Number of customers served	20,000
Number of producers served	300
Shares of common stock issued at closing (shares) | shares		592,970
Common stock issued at closing	$ 30,200	$ 30,164		30,164
Cash paid	27,500	27,494
Long-term debt	1,696	1,696		1,696
Cash acquired	6,800	6,806		6,806
Additional contingent cash consideration		$ 15,000		15,000
Period for revenue generated from potential new gathering opportunities		5 years
Transaction costs						$ 1,300
Revenues		$ 5,600		18,400
Net income		$ (563)		1,100
Diluted (in dollars per share) | $ / shares		$ 0.03
Goodwill	$ 11,100	$ 10,119		$ 10,119