Variable Interest Entities - Carry Amounts and Classification of Assets and Liabilities (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($) entity	Mar. 31, 2017	Jan. 31, 2017	Dec. 31, 2016 USD ($)
Variable interest entities
Variable Interest Entity [Line Items]
Number of variable interest entities, primary beneficiary | entity	9
VIE, primary beneficiary
Variable Interest Entity [Line Items]
Total assets	$ 557,562			$ 610,054
Total liabilities	501,417			549,090
VIE, primary beneficiary | Current assets
Variable Interest Entity [Line Items]
Total assets	177,766			186,739
VIE, primary beneficiary | Non-current assets
Variable Interest Entity [Line Items]
Total assets	379,796			423,315
VIE, primary beneficiary | Current liabilities
Variable Interest Entity [Line Items]
Total liabilities	390,603			386,297
VIE, primary beneficiary | Non-current liabilities
Variable Interest Entity [Line Items]
Total liabilities	$ 110,814			$ 162,793
SE 25
Variable Interest Entity [Line Items]
Percentage of voting interests acquired		100.00%
Millenium Solar Power
Variable Interest Entity [Line Items]
Additional ownership interest acquired			26.00%