Basis of Presentation and Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2018

Accounting Policies [Abstract]

Weighted-Average Valuation Assumptions

The Company used the following weighted-average assumptions in applying the Black-Scholes valuation model:

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018	2017
Risk-free interest rate	2.73%—2.77%		2.01% - 2.07%		2.49% - 2.77%	2.01% - 2.07%
Expected term (in years)	6.21—6.69		6.12—6.62		6.18—6.69	6.08—6.62
Expected dividend yield	—		—		—	—
Expected volatility	54.6	%	59.8	%	54.6% -55.1%	59.8% - 61.0%

Estimated Depreciable Lives of Property, Plant and Equipment

Depreciation is calculated using the straight-line method over the estimated depreciable lives of the respective assets as follows:

	Depreciable Lives
Energy Servers	15-21 years
Computers, software and hardware	3-5 years
Machinery and equipment	5-10 years
Furniture and fixtures	3-5 years
Leasehold improvements	1-5 years
Buildings	35 years

Property, plant and equipment, net consisted of the following (in thousands):

	June 30, 2018			December 31, 2017
Energy Servers	$	511,239		$	511,153
Computers, software and hardware	19,743			19,384
Machinery and equipment	98,397			97,158
Furniture and fixtures	4,695			4,679
Leasehold improvements	22,931			22,799
Building	40,512			40,512
Construction in progress	9,486			9,898
	707,003			705,583
Less: Accumulated depreciation	(229,238		)	(207,794		)
	$	477,765		$	497,789