Outstanding Loans and Security Agreements - Recourse Debt Facilities (Additional Information) (Details)		1 Months Ended	3 Months Ended	19 Months Ended
	May 31, 2013 USD ($)	Jul. 31, 2018 USD ($) shares	Mar. 31, 2019 USD ($) day $ / shares shares	Jun. 30, 2016 USD ($)	Dec. 31, 2018 USD ($)	Jan. 31, 2018	Jan. 18, 2018	Aug. 31, 2017 shares	Jun. 30, 2017 USD ($) agreement	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Sep. 10, 2016 USD ($)	Jan. 29, 2016 USD ($)	Dec. 15, 2015 USD ($) $ / shares	Dec. 31, 2014
Debt Instrument [Line Items]
Long-term debt carrying value			$ 741,078,000		$ 741,281,000
Unpaid principal balance			780,700,000		786,495,000
Long-term portion of debt			703,568,000		711,433,000
Indebtedness in excess of			$ 300,000
Issuance of common stock upon exercise of warrants (in shares) | shares			312,575
Credit facility | Term Loan due November 2020, Recourse
Debt Instrument [Line Items]
Debt face amount	$ 5,000,000.0									$ 5,000,000.0
Term loan | Term Loan due December 2021, Non-Recourse
Debt Instrument [Line Items]
Long-term debt carrying value			$ 122,701,000		123,384,000
Interest rate percentage			2.50%
Unpaid principal balance			$ 124,593,000		125,456,000
Long-term portion of debt			$ 118,926,000		$ 119,712,000
Term loan | Term Loan due November 2020, Recourse
Debt Instrument [Line Items]
Debt face amount	$ 12,000,000
Debt term	90 months
Weighted average interest rate (as a percentage)			6.50%		5.90%
Long-term debt carrying value			$ 2,795,000		$ 3,214,000
Interest rate percentage			4.00%
Unpaid principal balance			$ 2,857,000		3,286,000
Long-term portion of debt			1,112,000		1,528,000
Indebtedness in excess of			$ 100,000
Convertible promissory notes | Convertible Promissory Notes due December 2019 and 2020, Recourse
Debt Instrument [Line Items]
Interest rate percentage			5.00%
Unpaid principal balance		$ 221,600,000
Convertible promissory notes | Convertible Promissory Notes Interest Rate 5% Due December 2020, Recourse
Debt Instrument [Line Items]
Long-term debt carrying value			$ 35,136,000		34,706,000
Interest rate percentage			5.00%
Unpaid principal balance			$ 33,104,000		33,104,000
Long-term portion of debt			$ 35,136,000		34,706,000
Convertible promissory notes | Convertible Promissory Notes Interest Rate 8% Due December 2018
Debt Instrument [Line Items]
Debt term				3 years
Convertible promissory notes | Convertible Promissory Notes due December 2020, Recourse
Debt Instrument [Line Items]
Debt face amount												$ 75,000,000	$ 25,000,000	$ 160,000,000
Interest rate percentage			6.00%			6.00%
Convertible stock price (in dollars per share) | $ / shares			$ 20.61											$ 11.25
Convertible promissory notes | Convertible Promissory Notes Interest Rate 6% Due December 2020, Recourse
Debt Instrument [Line Items]
Long-term debt carrying value			$ 267,289,000		263,284,000
Interest rate percentage			6.00%
Convertible stock price (in dollars per share) | $ / shares			$ 11.25
Unpaid principal balance			$ 296,233,000		290,400,000
Long-term portion of debt			267,289,000		263,284,000
Notes | Notes due July 2024, Recourse
Debt Instrument [Line Items]
Debt face amount									$ 100,000,000
Long-term debt carrying value			$ 96,073,000		95,555,000
Interest rate percentage			10.00%						10.00%
Unpaid principal balance			$ 100,000,000		100,000,000
Long-term portion of debt			82,073,000		88,555,000
Number of agreements | agreement									5
Affiliated entity
Debt Instrument [Line Items]
Long-term debt carrying value			63,492,000		64,053,000
Unpaid principal balance			67,493,000		68,272,000
Long-term portion of debt			$ 61,151,000		61,853,000
Affiliated entity | Convertible promissory notes | Convertible Promissory Notes due December 2019 and 2020, Recourse
Debt Instrument [Line Items]
Debt face amount				$ 193,200,000.0
Interest rate percentage							8.00%								8.00%
Convertible stock price (in dollars per share) | $ / shares			$ 38.64
Affiliated entity | Convertible promissory notes | Convertible Promissory Notes due December 2020, Recourse
Debt Instrument [Line Items]
Debt face amount											$ 260,000,000
Interest rate percentage			6.00%						6.00%		5.00%
Percentage of debt outstanding to maintain as collateral			200.00%
Holders of debt, percentage subject to cross-acceleration provision			25.00%
Indebtedness in excess of			$ 15,000,000.0
Affiliated entity | Convertible promissory notes | Convertible Promissory Notes Interest Rate 6% Due December 2020, Recourse
Debt Instrument [Line Items]
Long-term debt carrying value			27,734,000		27,734,000
Unpaid principal balance			27,734,000		27,734,000
Long-term portion of debt			$ 27,734,000		$ 27,734,000
Affiliated entity | Convertible redeemable common stock warrants | CPPIB
Debt Instrument [Line Items]
Number of securities called by warrants (in shares) | shares								312,888
Maximum | Convertible redeemable common stock warrants | J.P. Morgan
Debt Instrument [Line Items]
Number of securities called by warrants (in shares) | shares			146,666
Maximum | Convertible redeemable common stock warrants | CPPIB
Debt Instrument [Line Items]
Number of securities called by warrants (in shares) | shares			166,222
Class B common stock
Debt Instrument [Line Items]
Debt conversion, shares issued (in shares) | shares		5,734,440
On or after July 27, 2020 | Affiliated entity | Convertible promissory notes | Convertible Promissory Notes due December 2020, Recourse
Debt Instrument [Line Items]
Last reported sale price of common stock (at least) (in dollars per share) | $ / shares			$ 22.50
Trading days (at least) | day			20
Period of consecutive trading days | day			30
Trading days immediately preceding redemption date | day			3