AMERICAN TOWER CORPORATION AND SUBSIDIARIES NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (Tabular amounts in millions, unless otherwise disclosed)
Accounts Receivable and Deferred Rent Asset—The Company derives the largest portion of its revenues and corresponding accounts receivable and the related deferred rent asset from a relatively small number of tenants in the telecommunications industry, and 54% of its current-year revenues are derived from four tenants.
The Company’s deferred rent asset is associated with non-cancellable tenant leases that contain fixed escalation clauses over the terms of the applicable lease in which revenue is recognized on a straight-line basis over the lease term.
The Company mitigates its concentrations of credit risk with respect to notes and trade receivables and the related deferred rent assets by actively monitoring the creditworthiness of its borrowers and tenants. In recognizing tenant revenue, the Company assesses the collectibility of both the amounts billed and the portion recognized in advance of billing on a straight-line basis. This assessment takes tenant credit risk and business and industry conditions into consideration to ultimately determine the collectibility of the amounts billed. To the extent the amounts, based on management’s estimates, may not be collectible, revenue recognition is deferred until such point as collectibility is determined to be reasonably assured. Any amounts that were previously recognized as revenue and subsequently determined to be uncollectible are charged to bad debt expense included in Selling, general, administrative and development expense in the accompanying consolidated statements of operations.
Accounts receivable is reported net of allowances for doubtful accounts related to estimated losses resulting from a tenant’s inability to make required payments and allowances for amounts invoiced whose collectibility is not reasonably assured. These allowances are generally estimated based on payment patterns, days past due and collection history, and incorporate changes in economic conditions that may not be reflected in historical trends, such as tenants in bankruptcy, liquidation or reorganization. Receivables are written-off against the allowances when they are determined to be uncollectible. Such determination includes analysis and consideration of the particular conditions of the account. Changes in the allowances were as follows:
(1) In 2019, write-offs are primarily related to uncollectible amounts in India. In 2018 and 2017, recoveries include recognition of revenue resulting from collections of previously reserved amounts.
Table:
 |  | Year Ended December 31, | 
 | 2019 | 2018 | 2017
Balance as of January 1, | $282.4 | $131.0 | $45.9
Current year increases | 104.3 | 157.8 | 87.2
Write-offs, recoveries and other (1) | (223.4) | (6.4) | (2.1)
Balance as of December 31, | $163.3 | $282.4 | $131.0


Question: Where does the company derive the largest portion of its revenues and corresponding accounts receivable and the related deferred rent asset from?
Answer: a relatively small number of tenants in the telecommunications industry, and 54% of its current-year revenues are derived from four tenants.