Transactions with Affiliates (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Amounts paid to the Williams Entities:
Percentage of ownership of affiliates of the company in the partnership	33.50%
Percentage of owner of company in affiliated partnership	25.80%
Affiliated Entity
Amounts received from the Williams Entities:
Services	$ 603	$ 622	$ 663
Insurance premiums and benefits	989	922	960
Reimbursed expenses	252	500	296
Amount received from Williams Entities	1,844	2,044	1,919
Amounts paid to the Williams Entities:
Rent	1,697	1,741	1,614
Business entertainment	155	155	205
Reimbursed expenses	135	226	204
Amounts paid to the Williams Entities	$ 1,987	$ 2,122	$ 2,023