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Summary of Significant Accounting Policies (Tables)
 12 Months Ended
Dec. 31, 2020
Accounting Policies [Abstract]  
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
1–7
Equipment
1–9
Breeding stock
2–4
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, 2020, 2019 and 2018 are set forth in the table below:
202020192018
Valuation assumptions
Expected dividend yield0%0%0%
Expected volatility
59%–90%
58%–64%
55%–59%
Expected term (years)
6.00–10.00
6.256.25
Risk-free interest rate
0.36%–1.80%
1.53%–2.58%
2.33%–3.06%
Accounts Receivable, Allowance for Credit Losses
The following table shows the activity in the allowance for credit losses for the years ended December 31, 2020, 2019, and 2018:
 202020192018
Beginning balance$7,513 $4,991 $4,631 
Charged to operating expenses899 3,384 1,627 
Write offs of accounts receivable, net of recoveries(2,078)(862)(1,267)
Ending balance$6,334 $7,513 $4,991