VIE Arrangements - Carrying Amounts and Classification of the VIEs' Assets and Liabilities Included in the Consolidated Balance Sheets (Details) $ in Thousands		3 Months Ended
		Mar. 31, 2019 USD ($) InvestmentFund fund	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Current assets:
Cash		$ 245,604		$ 226,625
Restricted cash		64,182		77,626
Accounts receivable, net		67,522		66,435	$ 66,400
Prepaid expenses and other current assets		9,568		8,563
Total current assets		463,060		461,413
Solar energy systems, net		3,976,504		3,820,017
Other assets		367,951		335,685
Total assets	[1]	4,939,682		4,749,787
Current liabilities:
Accounts payable		105,977		131,278
Distributions payable to noncontrolling interests and redeemable noncontrolling interests		15,628		15,847
Accrued expenses and other liabilities		103,764		98,636
Deferred revenue, current portion		55,795		47,407
Deferred grants, current portion		7,961		7,885
Non-recourse debt, current portion		26,937		35,484
Total current liabilities		336,802		372,191
Deferred revenue, net of current portion		637,666		544,218
Deferred grants, net of current portion		219,583		221,739
Non-recourse debt, net of current portion		1,558,250		1,466,438
Other liabilities		84,068		48,210
Total liabilities (1)	[1]	$ 3,499,955		3,340,703
Number of pass-through Fund arrangements | InvestmentFund		3
Payments to acquire interest in VIEs		$ 4,600	$ 0
Acquisition of Variable Interest Entity		4,989
Additional Paid-In Capital
Current liabilities:
Acquisition of Variable Interest Entity		(1,077)
Variable Interest Entities
Current assets:
Cash		135,548		105,494
Restricted cash		969		2,071
Accounts receivable, net		16,988		18,539
Prepaid expenses and other current assets		386		387
Total current assets		153,891		126,491
Solar energy systems, net		2,761,312		2,712,377
Other assets		66,707		66,427
Total assets		2,981,910		2,905,295
Current liabilities:
Accounts payable		10,979		12,136
Distributions payable to noncontrolling interests and redeemable noncontrolling interests		15,545		15,797
Accrued expenses and other liabilities		7,315		7,122
Deferred revenue, current portion		33,504		29,102
Deferred grants, current portion		982		982
Non-recourse debt, current portion		4,336		4,217
Total current liabilities		72,661		69,356
Deferred revenue, net of current portion		405,261		367,818
Deferred grants, net of current portion		27,982		28,247
Non-recourse debt, net of current portion		184,958		186,494
Other liabilities		10,733		8,843
Total liabilities (1)		$ 701,595		$ 660,758
Number of pass-through Fund arrangements | fund		6
Payments to acquire interest in VIEs		$ 4,600
Variable Interest Entities | Additional Paid-In Capital
Current liabilities:
Acquisition of Variable Interest Entity		$ 1,100

[1] The Company’s consolidated assets as of March 31, 2019 and December 31, 2018 include $2,981,910 and $2,905,295, respectively, in assets of variable interest entities (“VIEs”) that can only be used to settle obligations of the VIEs. These assets include solar energy systems, net, as of March 31, 2019 and December 31, 2018 of $2,761,312 and $2,712,377, respectively; cash as of March 31, 2019 and December 31, 2018 of $135,548 and $105,494, respectively; restricted cash as of March 31, 2019 and December 31, 2018 of $969 and $2,071, respectively; accounts receivable, net as of March 31, 2019 and December 31, 2018 of $16,988 and $18,539, respectively; prepaid expenses and other current assets as of March 31, 2019 and December 31, 2018 of $386 and $387, respectively; and other assets as of March 31, 2019 and December 31, 2018 of $66,707 and $66,427, respectively. The Company’s consolidated liabilities as of March 31, 2019 and December 31, 2018 include $701,595 and $660,758, respectively, in liabilities of VIEs whose creditors have no recourse to the Company. These liabilities include accounts payable as of March 31, 2019 and December 31, 2018 of $10,979 and $12,136, respectively; distributions payable to noncontrolling interests and redeemable noncontrolling interests as of March 31, 2019 and December 31, 2018 of $15,545 and $15,797, respectively; accrued expenses and other current liabilities as of March 31, 2019 and December 31, 2018 of $7,315 and $7,122, respectively; deferred revenue as of March 31, 2019 and December 31, 2018 of $438,765 and $396,920, respectively; deferred grants as of March 31, 2019 and December 31, 2018 of $28,964 and $29,229, respectively; non-recourse debt as of March 31, 2019 and December 31, 2018 of $189,294 and $190,711, respectively; and other liabilities as of March 31, 2019 and December 31, 2018 of $10,733 and $8,843, respectively.