Consolidated Variable Interest Entities - Balance Sheets (Details) - Variable Interest Entity, Primary Beneficiary - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Cash and cash equivalents
Variable Interest Entity [Line Items]
Assets	$ 12,787	$ 60,453
Accounts receivable
Variable Interest Entity [Line Items]
Assets	21,261	20,662
Prepaid expenses and other
Variable Interest Entity [Line Items]
Assets	2,320	5,745
Property, plant and equipment, net
Variable Interest Entity [Line Items]
Assets	2,696,154	2,578,834
Other assets
Variable Interest Entity [Line Items]
Assets	281,993	206,104
Accounts payable
Variable Interest Entity [Line Items]
Liabilities	42,755	35,831
Other current liabilities
Variable Interest Entity [Line Items]
Liabilities	41,589	32,242
Long-term debt
Variable Interest Entity [Line Items]
Liabilities	986,542	985,732
Other liabilities and credits
Variable Interest Entity [Line Items]
Liabilities	$ 9,974	$ 9,562