Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Rollforward of Allowance for Doubtful Accounts

The following table shows the activity in the allowance for doubtful receivable accounts from continuing operations for the years ended December 31, 2019, 2018, and 2017:

	2019			2018			2017
Beginning balance	$	4,991		$	4,631		$	3,703
Charged to operating expenses	3,384			1,627			1,217
Write offs of accounts receivable, net of recoveries	(862		)	(1,267		)	(289		)
Ending balance	$	7,513		$	4,991		$	4,631

Estimated Useful Lives of Property, Plant and Equipment

The estimated useful lives of these assets from continuing operations are as follows:

	Years
Land improvements	4-15
Buildings and building improvements	3-23
Furniture and fixtures	1–10
Equipment	1–9
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 fourteen 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, 2019, 2018 and 2017 are set forth in the table below:

	2019	2018	2017
Valuation assumptions
Expected dividend yield	0%	0%	0%
Expected volatility	58%—64%	55%—59%	57%—60%
Expected term (years)	6.25	6.25	6.25
Risk-free interest rate	1.53%—2.58%	2.33%—3.06%	1.89%—2.27%