Annual report pursuant to Section 13 and 15(d)

Credit Facilities - Additional Information (Details)

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Credit Facilities - Additional Information (Details)
12 Months Ended
Feb. 27, 2020
Dec. 31, 2019
USD ($)
Line of Credit Facility [Line Items]    
Revolving credit facility   $ 40,000,000
Financial covenants, minimum current assets to current liabilities ratio   1.25
Financial covenants, minimum net worth   $ 130,000,000
Debt instrument, covenant terms percent of proceeds from stock issuance added to net worth requirement (percentage)   100.00%
Minimum cash, cash equivalents, and short-term investments   $ 69,600,000
Financial covenant, maximum funded debt to tangible net worth ratio   0.50
Outstanding borrowings under our Credit Agreement   $ 0
Total outstanding letters of credit   10,200,000
Remaining borrowing capacity on line of credit   29,800
Tangible net worth   $ 153,400,000
Current ratio   1.67
Funded debt to tangible net worth ratio   0.07
Surety bonds   $ 409,900,000
Letter of Credit | Prime Rate    
Line of Credit Facility [Line Items]    
Basis spread on variable rate (percentage)   4.75%
Letter of Credit | London Interbank Offered Rate (LIBOR)    
Line of Credit Facility [Line Items]    
Basis spread on variable rate (percentage)   1.76%
Letter of Credit | Subsequent Event    
Line of Credit Facility [Line Items]    
Stated interest rate (percentage) 2.00%  
Letter of Credit | Subsequent Event | London Interbank Offered Rate (LIBOR)    
Line of Credit Facility [Line Items]    
Basis spread on variable rate (percentage) 2.00%  
Revolving Credit Facility | Subsequent Event    
Line of Credit Facility [Line Items]    
Fees on undrawn borrowings (percentage) 0.40%  
Minimum    
Line of Credit Facility [Line Items]    
Minimum cash, cash equivalents, and short-term investments   $ 40,000,000