Fair Value

Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis

The tables below sets forth, by level, our financial assets that were accounted for at fair value for the respective periods. The table does not include assets and liabilities that are measured at historical cost or any basis other than fair value (in thousands):



	Fair Value Measured at Reporting Date Using
March 31, 2019	Level 1		Level 2		Level 3		Total
Assets
Cash equivalents:
Money market funds	$	217,258	$	—	$	—	$	217,258
Interest rate swap agreements	—		27		—		27
	$	217,258	$	27	$	—	$	217,285
Liabilities
Accrued other current liabilities	$	1,723	$	—	$	—	$	1,723
Derivatives:
Natural gas fixed price forward contracts	—		—		8,796		8,796
Interest rate swap agreements¹	—		5,719		—		5,719
	$	1,723	$	5,719	$	8,796	$	16,238

¹As of March 31, 2019, $0.1 million of the gain on the interest rate swaps accumulated in other comprehensive income (loss) is expected to be reclassified into earnings in the next twelve months.



	Fair Value Measured at Reporting Date Using
December 31, 2018	Level 1		Level 2		Level 3		Total
Assets
Cash equivalents:
Money market funds	$	143,843	$	—	$	—	$	143,843
Short-term investments	104,350		—		—		104,350
Interest rate swap agreements	—		82		—		82
	$	248,193	$	82	$	—	$	248,275
Liabilities
Accrued other current liabilities	$	1,331	$	—	$	—	$	1,331
Derivatives:
Natural gas fixed price forward contracts	—		—		9,729		9,729
Interest rate swap agreements	—		3,630		—		3,630
	$	1,331	$	3,630	$	9,729	$	14,690

The following table provides the fair value of our natural gas fixed price contracts (dollars in thousands):



	March 31,			December 31,
	2019			2018
	Number of Contracts (MMBTU)²	Fair Value		Number of Contracts (MMBTU)²	Fair Value

Liabilities¹
Natural gas fixed price forward contracts (not under hedging relationships)	2,873	$	8,796	3,096	$	9,729

¹ Recorded in current liabilities and derivative liabilities in the condensed consolidated balance sheets.
² One MMBTU, or one million British Thermal Units, is a traditional unit of energy used to describe the heat value (energy content) of fuels.

For the three months ended March 31, 2019 and 2018, we marked-to-market the fair value of its fixed price natural gas forward contracts and recorded a gain of $0.4 million and a loss of $0.9 million, respectively, and recorded gains on the settlement of these contracts of $0.5 million and $1.1 million, respectively, in cost of revenue on the condensed consolidated statement of operations.

Embedded Derivative on 6% Convertible Promissory Notes - Between December 2015 and September 2016, we issued $260.0 million convertible promissory notes due December 2020 ("6% Notes") to certain investors. The 6% Notes bore a 5% fixed interest rate, payable monthly either in cash or in kind, at our election. We amended the terms of the 6% Notes in June 2017 to reduce the collateral securing the notes and to increase the interest rate from 5% to 6%. The 6% Notes are convertible at the option of the holders at a conversion price of $11.25 per share. Upon the IPO, the final value of the conversion feature was $177.2 million and was reclassified from a derivative liability to additional paid-in capital.

There were no transfers between fair value measurement classifications during the periods ended March 31, 2019 and 2018. The changes in the Level 3 financial assets were as follows (in thousands):



	Natural Gas Fixed Price Forward Contracts			Preferred Stock Warrants		Embedded Derivative Liability		Total
Balances at December 31, 2018	$	9,729		$	—	$	—	$	9,729
Settlement of natural gas fixed price forward contracts	(527		)	—		—		(527		)
Changes in fair value	(406		)	—		—		(406		)
Balances at March 31, 2019	$	8,796		$	—	$	—	$	8,796



	Natural Gas Fixed Price Forward Contracts			Preferred Stock Warrants			Embedded Derivative Liability		Total
Balances at December 31, 2017	$	15,368		$	9,825		$	140,771	$	165,964
Settlement of natural gas fixed price forward contracts	(1,102		)	—			—		(1,102		)
Changes in fair value	855			(3,271		)	9,732		7,316
Balances at March 31, 2018	$	15,121		$	6,554		$	150,503	$	172,178

Significant changes in any assumption input in isolation can result in a significant change in fair value measurement. Generally, an increase in the market price of our shares of common stock, an increase in natural gas prices, an increase in the volatility of ours shares of common stock and an increase in the remaining term of the conversion feature would each result in a directionally similar change in the estimated fair value of our derivative liability. Increases in such assumption values would increase the associated liability while decreases in these assumption values would decrease the associated liability. An increase in the risk-free interest rate or a decrease in the market price of our shares of common stock would result in a decrease in the estimated fair value measurement and thus a decrease in the associated liability.

Financial Assets and Liabilities Not Measured at Fair Value on a Recurring Basis

Customer Receivables and Debt Instruments - We estimate fair value for customer financing receivables, senior secured notes, term loans and convertible promissory notes based on rates currently offered for instruments with similar maturities and terms (Level 3). The following table presents the estimated fair values and carrying values of customer receivables and debt instruments (in thousands):



	March 31, 2019				December 31, 2018
	Net Carrying Value		Fair Value		Net Carrying Value		Fair Value

Customer receivables:
Customer financing receivables	$	71,337	$	51,312	$	72,676	$	51,541
Debt instruments:
Recourse
LIBOR + 4% term loan due November 2020	2,795		2,914		3,214		3,311
5% convertible promissory note due December 2020	35,136		33,832		34,706		31,546
6% convertible promissory notes due December 2020	267,289		418,999		263,284		353,368
10% notes due July 2024	96,073		99,598		95,555		99,260
Non-recourse
5.22% senior secured notes due March 2025	75,786		79,341		78,566		80,838
7.5% term loan due September 2028	35,758		41,759		36,319		39,892
LIBOR + 5.25% term loan due October 2020	23,734		25,679		23,916		25,441
6.07% senior secured notes due March 2030	81,806		88,715		82,337		85,917
LIBOR + 2.5% term loan due December 2021	122,701		125,770		123,384		123,040

Long-Lived Assets - Our long-lived assets include property, plant and equipment. The carrying amounts of our long-lived assets are periodically reviewed for impairment whenever events or changes in circumstances indicate that the carrying value of these assets may not be recoverable or that the useful life is shorter than originally estimated. No material impairment of any long-lived assets was identified in the three months ended March 31, 2019 and 2018.