Commitments, Contingencies and Uncertainties (Power Purchase and Sale Agreement) (Details)	12 Months Ended
	Dec. 31, 2016 MW
Freeport Agreement 3 - 25 MW
Long-term Purchase Commitment [Line Items]
Long-Term Purchase commitment, Maximum Quantity	25
Long-term Purchase Commitment, Time Period	10 years 1 month
Long-Term Sale Commitment, Maximum Quantity	25
Long-Term Sale Commitment, Time Period	10 years 1 month
Freeport Agreement 2 - 100 MW
Long-term Purchase Commitment [Line Items]
Long-Term Purchase commitment, Maximum Quantity	100
Long-term Purchase Commitment, Time Period	15 years 7 months
Long-Term Sale Commitment, Maximum Quantity	100
Long-Term Sale Commitment, Time Period	15 years 7 months
Hatch Solar Energy Center I
Long-term Purchase Commitment [Line Items]
Long-Term Purchase commitment, Maximum Quantity	5
Long-term Purchase Commitment, Time Period	25 years
Plant Commercial Operation Date	Jul. 01, 2011
NRG
Long-term Purchase Commitment [Line Items]
Long-Term Purchase commitment, Maximum Quantity	20
Long-term Purchase Commitment, Time Period	20 years 1 month
Plant Commercial Operation Date	Aug. 01, 2011
Sun Edison 1
Long-term Purchase Commitment [Line Items]
Long-Term Purchase commitment, Maximum Quantity	10
Long-term Purchase Commitment, Time Period	25 years 1 month
Plant Commercial Operation Date	Jun. 25, 2012
Sun Edison 2
Long-term Purchase Commitment [Line Items]
Long-Term Purchase commitment, Maximum Quantity	12
Long-term Purchase Commitment, Time Period	25 years 1 month
Plant Commercial Operation Date	May 02, 2012
Macho Springs Solar
Long-term Purchase Commitment [Line Items]
Long-Term Purchase commitment, Maximum Quantity	50
Long-term Purchase Commitment, Time Period	20 years
Plant Commercial Operation Date	May 23, 2014
Plant Capacity	50
Newman Solar
Long-term Purchase Commitment [Line Items]
Long-Term Purchase commitment, Maximum Quantity	10
Long-term Purchase Commitment, Time Period	30 years
Plant Commercial Operation Date	Dec. 30, 2014
Freeport Agreement 1 - 125 MW
Long-term Purchase Commitment [Line Items]
Long-Term Purchase commitment, Maximum Quantity	125
Long-term Purchase Commitment, Time Period	2 years
Long-Term Sale Commitment, Maximum Quantity	125
Long-Term Sale Commitment, Time Period	2 years
Long-term Contract for Purchase of Electric Power, Date of Contract Expiration	Dec. 31, 2018
Long-Term Contract For Sale Of Electric Power Date Of Contract Expiration	Dec. 31, 2018
Sun Edison 1 and Sun Edison 2
Long-term Purchase Commitment [Line Items]
Solar Photovoltaic Projects, Number of Units	2
FERC | Freeport Agreement 1 - 125 MW
Long-term Purchase Commitment [Line Items]
Long-term Contract for Purchase of Electric Power, Date of Contract Expiration	Dec. 31, 2021
Long-Term Contract For Sale Of Electric Power Date Of Contract Expiration	Dec. 31, 2021