Power Purchase Agreement Programs - Schedule of PPA Entities' Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 91,596	$ 103,828
Restricted cash, current	25,860	44,387
Accounts receivable	36,804	30,317
Customer financing receivable	5,398	5,209
Total current assets	390,273	419,981
Property, plant and equipment, net	477,765	497,789
Customer financing receivable, non-current	69,963	72,677
Restricted cash, non-current	32,416	32,397
Other long-term assets	38,386	37,460
Total assets	1,157,737	1,220,987
Current liabilities
Accounts payable	53,798	48,582
Accrued other current liabilities	54,832	67,649
Deferred revenue and customer deposits	94,582	118,106
Current portion of debt	30,006	20,136
Total current liabilities	248,146	271,284
Derivative liabilities	188,199	156,552
Deferred revenue and customer deposits	301,550	309,843
Long-term portion of debt	930,123	921,205
Other long-term liabilities	52,153	52,915
Total liabilities	1,722,540	1,721,624
Variable Interest Entity, Primary Beneficiary
Current assets
Cash and cash equivalents	9,691	9,549
Restricted cash, current	4,735	7,969
Accounts receivable	7,293	7,680
Customer financing receivable	5,398	5,209
Prepaid expenses and other current assets	1,802	6,365
Total current assets	28,919	36,772
Property, plant and equipment, net	414,684	430,464
Customer financing receivable, non-current	69,963	72,677
Restricted cash, non-current	27,604	26,748
Other long-term assets	4,423	3,767
Total assets	545,593	570,428
Current liabilities
Accounts payable	482	520
Accrued other current liabilities	1,569	2,378
Deferred revenue and customer deposits	786	786
Current portion of debt	19,655	18,446
Total current liabilities	22,492	22,130
Derivative liabilities	2,528	5,060
Deferred revenue and customer deposits	9,092	9,482
Long-term portion of debt	333,102	342,050
Other long-term liabilities	1,514	1,226
Total liabilities	$ 368,728	$ 379,948