Power Purchase Agreement Programs - Schedule of PPA Entities' Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 395,516	$ 103,828
Restricted cash, current	17,931	44,387
Accounts receivable	41,485	30,317
Customer financing receivable	5,496	5,209
Total current assets	698,532	419,981
Property, plant and equipment, net	471,074	497,789
Non-current portion of investment in sales-type financing leases	68,535	72,677
Restricted cash, non-current	30,779	32,397
Other long-term assets	37,008	37,460
Total assets	1,445,145	1,220,987
Current liabilities
Accounts payable	59,818	48,582
Accrued other current liabilities	66,873	67,649
Deferred revenue and customer deposits	105,265	118,106
Current portion of debt	21,922	20,136
Total current liabilities	271,853	271,284
Derivative liabilities	9,441	156,552
Deferred revenue and customer deposits	290,481	309,843
Long-term portion of debt	718,889	921,205
Other long-term liabilities	48,161	52,915
Total liabilities	1,338,825	1,721,624
Variable Interest Entity, Primary Beneficiary
Current assets
Cash and cash equivalents	5,496	9,549
Restricted cash, current	3,252	7,969
Accounts receivable	7,377	7,680
Customer financing receivable	5,496	5,209
Prepaid expenses and other current assets	5,727	6,365
Total current assets	27,348	36,772
Property, plant and equipment, net	406,784	430,464
Non-current portion of investment in sales-type financing leases	68,535	72,677
Restricted cash, non-current	27,778	26,748
Other long-term assets	4,702	3,767
Total assets	535,147	570,428
Current liabilities
Accounts payable	549	520
Accrued other current liabilities	1,145	2,378
Deferred revenue and customer deposits	786	786
Current portion of debt	20,235	18,446
Total current liabilities	22,715	22,130
Derivative liabilities	1,826	5,060
Deferred revenue and customer deposits	8,894	9,482
Long-term portion of debt	328,358	342,050
Other long-term liabilities	1,656	1,226
Total liabilities	$ 363,449	$ 379,948