Commitments and Contingencies Commitments and Contingencies (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	24 Months Ended
	Apr. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Consent Decree [Member]
Other Commitments [Line Items]
Civil penalty		$ 4,950	$ 54,700
Mitigation projects		4,500
Supplemental environmental projects		$ 4,000
Subsequent Event [Member]
Other Commitments [Line Items]
Reduced penalty	$ 124
Maximum penalty reduction	80.00%