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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount, before accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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Amount of debt for which creditor does not have general recourse to the debtor but rather has recourse only to the property used for collateral in the transaction or other specific property.

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Amount of transaction price allocated to performance obligation that has not been recognized as revenue.

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DESCRIPTION OF OPERATIONS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenues and Notes Payable (Details) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	Aug. 31, 2017	May 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Apr. 30, 2014
Revenue recognition
Allowance for doubtful accounts			$ 0
Amortization of Debt Issuance Costs from Non-Recourse Notes Due 2029
Payment of principal on non-recourse notes due 2029			487,189	$ 6,828	$ 0
Loss on extinguishment debt			(7,256)	2,342	$ 0
Income Taxes
Unrecognized tax benefits would affect our effective income tax rate if recognized			0
Non-Recourse Notes \| 2029 Notes
Amortization of Debt Issuance Costs from Non-Recourse Notes Due 2029
Payment of principal on non-recourse notes due 2029	$ 407,600	$ 50,000	29,600	$ 6,800
Loss on extinguishment debt	$ (7,300)
Non-Recourse Notes \| Private Placement \| 2029 Notes
Amortization of Debt Issuance Costs from Non-Recourse Notes Due 2029
Non-Recourse Debt						$ 450,000
Interest rate (as a percent)						9.00%
Debt issuance costs						$ 15,300
Strategic alliance - MABA program license
Revenue recognition
Remaining deferred revenue performance obligation			$ 0