Summary of Significant Accounting Policies - Deferred Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Deferred Revenue Arrangement [Line Items]
Deferred revenue	$ 693,461		$ 591,625	$ 564,900
Deferred revenue, revenue recognized	14,000	$ 12,800
Contracted but not yet recognized	$ 5,600,000
Revenue expected to recognize over next twelve months, percent	6.00%
Revenue recognized, term, existing deferred revenue	10 years
Customer agreement, initial term	22 years
Deferred revenue, increase (decrease)	$ 101,848	$ 7,456
Under Customer Agreements
Deferred Revenue Arrangement [Line Items]
Deferred revenue	$ 583,522		576,727
Under Customer Agreements | Solar energy systems
Deferred Revenue Arrangement [Line Items]
Average age	4 years
Under Customer Agreements | Payments received
Deferred Revenue Arrangement [Line Items]
Deferred revenue	$ 543,945		538,926
Under Customer Agreements | Financing component balance
Deferred Revenue Arrangement [Line Items]
Deferred revenue	39,577		$ 37,801
Under SREC contracts
Deferred Revenue Arrangement [Line Items]
Deferred revenue, increase (decrease)	$ 95,500
Minimum
Deferred Revenue Arrangement [Line Items]
Customer agreement, initial term	20 years
Minimum | Under SREC contracts
Deferred Revenue Arrangement [Line Items]
Customer agreement, initial term	10 years
Maximum
Deferred Revenue Arrangement [Line Items]
Customer agreement, initial term	25 years
Maximum | Under SREC contracts
Deferred Revenue Arrangement [Line Items]
Customer agreement, initial term	15 years