Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) Customer	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) Customer	Feb. 28, 2017 USD ($)	May 31, 2014 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Deferred revenue recognized			$ 60,300,000
Deferred revenue recognized in next 12 months			284,700,000
Deferred revenue related to sales of automotive regulatory credits	$ 0		0		$ 0
Automotive leasing	220,461,000	$ 286,158,000	633,713,000	$ 813,462,000
Maximum repurchase price of vehicles under resale value arrangement	629,100,000		629,100,000
Resale value exercisable by leasing partners	388,800,000		388,800,000
Resale value guarantees, current portion sales to customers	162,300,000		162,300,000
Resale value guarantees, lease revenue recognized	30,000,000		106,700,000
Unrecognized tax benefits	254,300,000		254,300,000		198,700,000
Unrecognized tax benefits, that would not affect effective tax rate	245,100,000		$ 245,100,000		$ 191,000,000
Number of customers representing more than ten percentage of accounts receivable | Customer			1		0
Accounts receivable from OEM customers excess percentage			10.00%		10.00%
Solar Energy Systems [Member]
Summary Of Significant Accounting Policies [Line Items]
Product warranty description			we also provide a warranty on the installation and components of the solar energy systems we sell for periods typically between 10 to 30 years.
Operating Lease Vehicles [Member]
Summary Of Significant Accounting Policies [Line Items]
Warranty costs incurred for operating lease vehicles collateralized debt arrangements	$ 4,600,000	10,800,000	$ 17,400,000	24,300,000
Recourse debt [Member] | 0.25% Convertible Senior Notes due in 2019 ("2019 Notes") [Member]
Summary Of Significant Accounting Policies [Line Items]
Interest Rate	0.25%		0.25%		0.25%
Maturity Dates			Mar. 31, 2019		Mar. 31, 2019
Recourse debt [Member] | 1.25% Convertible Senior Notes due in 2021 ("2021 Notes") [Member]
Summary Of Significant Accounting Policies [Line Items]
Interest Rate	1.25%		1.25%		1.25%
Maturity Dates			Mar. 31, 2021		Mar. 31, 2021
Recourse debt [Member] | 2.375% Convertible Senior Notes due in 2022 [Member]
Summary Of Significant Accounting Policies [Line Items]
Interest Rate	2.375%		2.375%		2.375%
Maturity Dates			Mar. 31, 2022		Mar. 31, 2022
Customer payments [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred upfront payments	$ 212,200,000		$ 212,200,000		$ 206,800,000
Customer payments [Member] | Energy Generation and Storage [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred revenue recognized			36,700,000
Deferred revenue recognized in next 12 months			6,700,000
Deferred upfront payments	158,700,000		158,700,000		124,000,000
Unbilled transaction price allocated to performance obligations, expected of more than one year	$ 115,700,000		$ 115,700,000
Deferred revenue, expected to recognize period	30 years		30 years
Rebates and Incentives [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred upfront payments	$ 31,800,000		$ 31,800,000		27,200,000
Sales To Leasing Companies With Guarantee [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred upfront payments	112,500,000		112,500,000
Automotive leasing	89,400,000		256,600,000
Resale value guarantee	734,300,000		$ 734,300,000
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Direct lease term			48 months
Deferred lease revenue [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred upfront payments	110,000,000		$ 110,000,000		$ 96,600,000
Automotive leasing	$ 101,100,000	$ 57,200,000	270,400,000	$ 155,900,000
Adoption of ASU 2014-09 [Member]
Summary Of Significant Accounting Policies [Line Items]
Increase in collateralized lease repayments			(304,400,000)
Payments from collateralized lease borrowings			38,700,000
Payments from collateralized lease borrowings			$ 343,100,000
Increase (decrease) in accumulated deficit and additional paid-in-capital							$ (623,200,000)
Accounting Standards Update 2017-05 [Member]
Summary Of Significant Accounting Policies [Line Items]
Increase (decrease) in accumulated deficit and additional paid-in-capital						$ (9,400,000)