Convertible and Long-Term Debt Obligations - Summary of Debt (Detail) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
	Aug. 16, 2018	Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 10,897,018	$ 10,167,380
Net Carrying Value, Current		1,833,475	799,849
Net Carrying Value, Long - Term		8,665,163	8,828,985
Unused Committed Amount		1,059,628	1,613,856
Solar asset-backed notes [Member]
Debt Instrument [Line Items]
Net Carrying Value, Long - Term		857,721	880,415
Solar Loan-backed Notes [Member]
Debt Instrument [Line Items]
Net Carrying Value, Long - Term		202,938	236,844
Recourse debt [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance		7,597,208	7,239,233
Net Carrying Value, Current		1,136,243	350,565
Net Carrying Value, Long - Term		6,114,374	6,404,811
Unused Committed Amount		229,173	729,929
Recourse debt [Member] | 0.25% Convertible Senior Notes due in 2019 ("2019 Notes") [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance		920,000	920,000
Net Carrying Value, Current		$ 901,453
Net Carrying Value, Long - Term			$ 869,092
Interest Rate		0.25%	0.25%
Contractual Maturity Date		Mar. 31, 2019	Mar. 31, 2019
Recourse debt [Member] | 1.25% Convertible Senior Notes due in 2021 ("2021 Notes") [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 1,380,000	$ 1,380,000
Net Carrying Value, Long - Term		$ 1,228,719	$ 1,186,131
Interest Rate		1.25%	1.25%
Contractual Maturity Date		Mar. 31, 2021	Mar. 31, 2021
Recourse debt [Member] | 2.375% Convertible Senior Notes due in 2022 [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 977,500	$ 977,500
Net Carrying Value, Long - Term		$ 863,771	$ 841,973
Interest Rate		2.375%	2.375%
Contractual Maturity Date		Mar. 31, 2022	Mar. 31, 2022
Recourse debt [Member] | 5.30% Senior Notes due in 2025 ("2025 Notes") [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 1,800,000	$ 1,800,000
Net Carrying Value, Long - Term		$ 1,777,948	$ 1,775,550
Interest Rate		5.30%	5.30%
Contractual Maturity Date		Aug. 31, 2025	Aug. 31, 2025
Recourse debt [Member] | Credit Agreement [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 1,593,000	$ 1,109,000
Net Carrying Value, Long - Term		1,593,000	1,109,000
Unused Committed Amount		$ 229,173	$ 729,929
Debt instrument interest rate description		1% plus LIBOR	1% plus LIBOR
Contractual Maturity Date		Jun. 30, 2020	Jun. 30, 2020
Recourse debt [Member] | Vehicle and other Loans [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 2,425	$ 16,205
Net Carrying Value, Current		$ 2,425	15,944
Net Carrying Value, Long - Term			$ 261
Contractual Maturity Date, Start		Oct. 31, 2018	Jan. 31, 2018
Contractual Maturity Date, End		Sep. 30, 2019	Sep. 30, 2019
Recourse debt [Member] | Vehicle and other Loans [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest Rate		1.80%	1.80%
Recourse debt [Member] | Vehicle and other Loans [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest Rate		7.60%	7.60%
Recourse debt [Member] | 2.75% Convertible Senior Notes due in 2018 [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 230,000	$ 230,000
Net Carrying Value, Current		$ 231,687	$ 222,171
Interest Rate		2.75%	2.75%
Contractual Maturity Date		Nov. 30, 2018	Nov. 30, 2018
Recourse debt [Member] | 1.625% Convertible Senior Notes due in 2019 [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 566,000	$ 566,000
Net Carrying Value, Long - Term		$ 535,668	$ 511,389
Interest Rate		1.625%	1.625%
Contractual Maturity Date		Nov. 30, 2019	Nov. 30, 2019
Recourse debt [Member] | Zero-Coupon Convertible Senior Notes due in 2020 [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 103,000	$ 103,000
Net Carrying Value, Long - Term		$ 90,427	$ 86,475
Interest Rate		0.00%	0.00%
Contractual Maturity Date		Dec. 31, 2020	Dec. 31, 2020
Recourse debt [Member] | Solar Bonds [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 25,283	$ 32,016
Net Carrying Value, Current		678	7,008
Net Carrying Value, Long - Term		$ 24,841	$ 24,940
Contractual Maturity Date, Start		Oct. 31, 2018	Mar. 31, 2018
Contractual Maturity Date, End		Jan. 31, 2031	Jan. 31, 2031
Recourse debt [Member] | Solar Bonds [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest Rate		2.60%	2.60%
Recourse debt [Member] | Solar Bonds [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest Rate		5.75%	5.80%
Recourse debt [Member] | 1.50% Convertible Senior Notes due in 2018 ("2018 Notes") [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance			$ 5,512
Net Carrying Value, Current			$ 5,442
Interest Rate			1.50%
Contractual Maturity Date			Jun. 30, 2018
Recourse debt [Member] | Related Party Promissory Notes due in February 2018 [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance			$ 100,000
Net Carrying Value, Current			$ 100,000
Interest Rate			6.50%
Contractual Maturity Date			Feb. 28, 2018
Non-recourse debt [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 3,299,810	$ 2,928,147
Net Carrying Value, Current		697,232	449,284
Net Carrying Value, Long - Term		2,550,789	2,424,174
Unused Committed Amount		830,455	883,927
Non-recourse debt [Member] | Warehouse Agreements [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance		659,388	673,811
Net Carrying Value, Current		110,204	195,382
Net Carrying Value, Long - Term		549,184	477,867
Unused Committed Amount		$ 440,612	$ 426,189
Interest Rate		3.50%	3.10%
Contractual Maturity Date	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019
Non-recourse debt [Member] | Canada Credit Facility [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 59,227	$ 86,708
Net Carrying Value, Current		29,297	31,106
Net Carrying Value, Long - Term		$ 29,930	$ 55,603
Contractual Maturity Date		Nov. 30, 2021	Nov. 30, 2021
Non-recourse debt [Member] | Canada Credit Facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest Rate		3.60%	3.60%
Non-recourse debt [Member] | Canada Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest Rate		5.10%	5.10%
Non-recourse debt [Member] | Term Loan due in December 2018 [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 181,746	$ 157,095
Net Carrying Value, Current		$ 181,452	156,884
Unused Committed Amount			$ 19,534
Interest Rate		5.80%	4.80%
Contractual Maturity Date		Dec. 31, 2018	Dec. 31, 2018
Non-recourse debt [Member] | Term Loan due in January 2021 [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 171,719	$ 176,290
Net Carrying Value, Current		6,527	5,885
Net Carrying Value, Long - Term		$ 164,389	$ 169,352
Interest Rate		5.80%	4.90%
Contractual Maturity Date		Jan. 31, 2021	Jan. 31, 2021
Non-recourse debt [Member] | Revolving Aggregation Credit Facility [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 210,157	$ 161,796
Net Carrying Value, Long - Term		207,718	158,733
Unused Committed Amount		$ 389,843	$ 438,204
Contractual Maturity Date		Dec. 31, 2019	Dec. 31, 2019
Non-recourse debt [Member] | Revolving Aggregation Credit Facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest Rate		5.00%	4.10%
Non-recourse debt [Member] | Revolving Aggregation Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest Rate		5.40%	4.50%
Non-recourse debt [Member] | Solar Renewable Energy Credit Loan Facility [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 31,501	$ 38,575
Net Carrying Value, Current		13,281	15,858
Net Carrying Value, Long - Term		$ 18,048	$ 22,774
Interest Rate		7.90%	7.30%
Contractual Maturity Date		Jul. 31, 2021	Jul. 31, 2021
Non-recourse debt [Member] | Cash equity debt [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 474,555	$ 482,133
Net Carrying Value, Current		10,932	12,334
Net Carrying Value, Long - Term		$ 448,938	$ 454,421
Contractual Maturity Date, Start		Jul. 31, 2033	Jul. 31, 2033
Contractual Maturity Date, End		Jan. 31, 2035	Jan. 31, 2035
Non-recourse debt [Member] | Cash equity debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest Rate		5.30%	5.30%
Non-recourse debt [Member] | Cash equity debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest Rate		5.80%	5.80%
Non-recourse debt [Member] | Solar asset-backed notes [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 883,806	$ 907,241
Net Carrying Value, Current		24,022	23,829
Net Carrying Value, Long - Term		$ 833,699	$ 856,586
Contractual Maturity Date, Start		Nov. 30, 2038	Nov. 30, 2038
Contractual Maturity Date, End		Feb. 29, 2048	Feb. 29, 2048
Non-recourse debt [Member] | Solar asset-backed notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest Rate		4.00%	4.00%
Non-recourse debt [Member] | Solar asset-backed notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest Rate		7.70%	7.70%
Non-recourse debt [Member] | Solar Loan-backed Notes [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 210,249	$ 244,498
Net Carrying Value, Current		9,888	8,006
Net Carrying Value, Long - Term		$ 193,050	$ 228,838
Contractual Maturity Date, Start		Sep. 30, 2048	Sep. 30, 2048
Contractual Maturity Date, End		Sep. 30, 2049	Sep. 30, 2049
Non-recourse debt [Member] | Solar Loan-backed Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest Rate		4.80%	4.80%
Non-recourse debt [Member] | Solar Loan-backed Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest Rate		7.50%	7.50%
Non-recourse debt [Member] | Automotive Asset-backed Notes [Member]
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 417,462
Net Carrying Value, Current		311,629
Net Carrying Value, Long - Term		$ 105,833
Contractual Maturity Date, Start		Dec. 31, 2019
Contractual Maturity Date, End		Mar. 31, 2021
Non-recourse debt [Member] | Automotive Asset-backed Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest Rate		2.30%
Non-recourse debt [Member] | Automotive Asset-backed Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest Rate		4.90%