Fair Value Measurements - Fair Value Level 3 Inputs, Quantitative Information (Details) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Apr. 21, 2017 USD ($)	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Fair Value, Measurements, Recurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Business Combination, Contingent Consideration, Liability	$ 21,502			$ 21,502
Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Business Combination, Contingent Consideration, Liability	21,502			21,502
Energy derivative [Member] | Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	33,895	$ 40,916		$ 33,895
Energy derivative [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate		1.52%		1.62%
Forward electricity price		81.76		77.10
Energy derivative [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate		1.00%		1.30%
Forward electricity price		15.83		14.75
Contingent Consideration Liability [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	21,502	$ 0		$ 21,502			$ 0
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)				200
Contingent Consideration Liability [Member] | Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	21,502			$ 21,502
Contingent Consideration Liability [Member] | Discounted Cash Flow [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Annual energy production loss				1.00%
Contingent Consideration Liability [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate				8.00%
Contingent Consideration Liability [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate				4.00%
Energy derivative [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	4,700		$ 9,300	$ 7,000	$ 14,200
Energy derivative [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	$ 33,895	$ 40,916	$ 49,531	$ 33,895	$ 49,531		$ 38,559	$ 58,858	$ 63,683
Broadview Project [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Business Combination, Contingent Consideration, Liability						$ 21,300