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Schedule II - Valuation and Qualifying Accounts (Notes)
 12 Months Ended
Dec. 31, 2020
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]  
SEC Schedule, 12-09, Schedule of Valuation and Qualifying Accounts Disclosure [Text Block]
Col. A Col. BCol. CCol. D Col. E
  Balance at
Beginning
of Period		Charged to
Costs and
Expenses		Charged to
Other Operating Revenue		Deductions
-Described		 Balance at
End of
Period
Year ended December 31, 2020
   Allowance for doubtful accounts$1,316 $567 $— $615 
2
$1,268 
   Allowance for revenue adjustments 1
737 — 4,751 4,483 
3
1,005 
Deferred tax valuation allowance395 — — — 395 
2,448 567 4,751 5,098 2,668 
Year ended December 31, 2019
   Allowance for doubtful accounts$1,290 $752 $— $726 
2
$1,316 
   Allowance for revenue adjustments 1
755 — 3,339 3,357 
3
737 
Deferred tax valuation allowance395 — — — 395 
2,440 752 3,339 4,083 2,448 
Year ended December 31, 2018
   Allowance for doubtful accounts$2,540 $122 $— $1,372 
2
$1,290 
   Allowance for revenue adjustments 1
451 — 3,624 3,320 
3
755 
Deferred tax valuation allowance360 35 — — 395 
3,351 157 3,624 4,692 2,440 
1 Represents an allowance for revenue adjustments to accounts receivable resulting from future billing rate changes.
2 Represents uncollectible accounts written off, net of recoveries.
3 Represents adjustments to billed accounts receivable