Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Summarized Financial Information of Equity Method Investments

Summarized financial data as of December 31, 2017 and 2016, and for the years ended December 31, 2017, 2016, and 2015, for the Company's equity method investments for which separate financial statements are not included, pursuant to SEC Regulation S-X Article 3-09, are shown in the following tables.



	December 31,
	2017		2016
Current assets	$	61,086	$	77,761
Non-current assets	13,598		11,040
Total assets	74,684		88,801
Current liabilities	6,213		11,588
Net assets	$	68,471	$	77,213



	Year Ended December 31,
	2017			2016			2015
Revenues, net	$	254		$	417		$	1,176
Operating expenses	41,904			62,373			32,513
Operating loss	(41,650		)	(61,956		)	(31,337		)
Other, net	(8		)	1,535			(64		)
Net loss	$	(41,658	)	$	(60,421	)	$	(31,401	)

Rollforward of Allowance for Doubtful Receivable Accounts

The following table shows the activity in the allowance for doubtful receivable accounts for the years ended December 31, 2017, 2016, and 2015:



	2017			2016			2015
Beginning balance	$	3,703		$	2,081		$	565
Charged to operating expenses	1,217			1,963			1,757
Write offs of accounts receivable, net of recoveries	(289		)	(341		)	(241		)
Ending balance	$	4,631		$	3,703		$	2,081

Estimated Useful Lives of Property, Plant and Equipment

The estimated useful lives of these assets are as follows:



	Years
Land improvements	4–20
Buildings and building improvements	3–25
Furniture and fixtures	1–10
Equipment	1–10
Breeding stock	1–4
Computer hardware and software	1–7

Leasehold improvements are amortized over the shorter of the useful life of the asset or the applicable lease term, generally one to twenty years.

Summary of Assumptions Used in Option Pricing Model

The assumptions used in the Black-Scholes option pricing model for the years ended December 31, 2017, 2016 and 2015 are set forth in the table below:



	2017	2016	2015
Valuation assumptions
Expected dividend yield	0%	0%	0%
Expected volatility	57%—60%	59%—60%	59%—62%
Expected term (years)	6.25	6.25	6.25
Risk-free interest rate	1.89%—2.27%	1.23%—2.17%	1.56%—1.95%