Related Party Transactions (Narrative) (Details) - O&G [Member]	3 Months Ended
	Mar. 31, 2018 agreement
Completed Infrastructure Projects [Member]
Related Party Transaction, Due from (to) Related Party [Abstract]
Number of joint ventures	2
Purple Line Segment 2 Expansion Project [Member]
Related Party Transaction, Due from (to) Related Party [Abstract]
Number of joint ventures	1
Ownership percentage in joint venture	75.00%
Related party's ownership percentage in joint venture	25.00%