Summary of Significant Accounting Policies (Changes to ARO) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Summary of Significant Accounting Policies [Abstract]
Balance beginning of year	$ 12,231	$ 12,074
Accretion	1,029	498	$ 534
Additions
Other		(341)
Balance end of year	$ 13,260	$ 12,231	$ 12,074