american tower corporation and subsidiaries notes to consolidated financial statements recognizing customer revenue , the company must assess the collectability of both the amounts billed and the portion recognized on a straight-line basis . this assessment takes customer credit risk and business and industry conditions into consideration to ultimately determine the collectability of the amounts billed . to the extent the amounts , based on management 2019s estimates , may not be collectible , recognition is deferred until such point as the uncertainty is resolved . any amounts which were previously recognized as revenue and subsequently determined to be uncollectible are charged to bad debt expense . accounts receivable are reported net of allowances for doubtful accounts related to estimated losses resulting from a customer 2019s inability to make required payments and reserves for amounts invoiced whose collectability 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 customers in bankruptcy , liquidation or reorganization . receivables are written-off against the allowances when they are determined uncollectible . such determination includes analysis and consideration of the particular conditions of the account . changes in the allowances were as follows for the years ended december 31 , ( in thousands ) : .
in 2009 what was the percentage change in the allowance balance for the uncollectable accounts
the company 2019s largest international customer is iusacell , which is the brand name under which a group of companies controlled by grupo iusacell , s.a . de c.v . ( 201cgrupo iusacell 201d ) operates . iusacell represented approximately 4% ( 4 % ) of the company 2019s total revenue for the year ended december 31 , 2010 . grupo iusacell has been engaged in a refinancing of a majority of its u.s . dollar denominated debt , and in connection with this process , two of the legal entities of the group , including grupo iusacell , voluntarily filed for a pre-packaged concurso mercantil ( a process substantially equivalent to chapter 11 of u.s . bankruptcy law ) with the backing of a majority of their financial creditors in december 2010 . as of december 31 , 2010 , iusacell notes receivable , net , and related assets ( which include financing lease commitments and a deferred rent asset that are primarily long-term in nature ) were $ 19.7 million and $ 51.2 million , respectively . functional currency 2014as a result of changes to the organizational structure of the company 2019s subsidiaries in latin america in 2010 , the company determined that effective january 1 , 2010 , the functional currency of its foreign subsidiary in brazil is the brazilian real . from that point forward , all assets and liabilities held by the subsidiary in brazil are translated into u.s . dollars at the exchange rate in effect at the end of the applicable reporting period . revenues and expenses are translated at the average monthly exchange rates and the cumulative translation effect is included in stockholders 2019 equity . the change in functional currency from u.s . dollars to brazilian real gave rise to an increase in the net value of certain non-monetary assets and liabilities . the aggregate impact on such assets and liabilities was $ 39.8 million with an offsetting increase in accumulated other comprehensive income ( loss ) . as a result of the renegotiation of the company 2019s agreements with its largest international customer , iusacell , which included , among other changes , converting all of iusacell 2019s contractual obligations to the company from u.s . dollars to mexican pesos , the company has determined that effective april 1 , 2010 , the functional currency of certain of its foreign subsidiaries in mexico is the mexican peso . from that point forward , all assets and liabilities held by those subsidiaries in mexico are translated into u.s . dollars at the exchange rate in effect at the end of the applicable reporting period . revenues and expenses are translated at the average monthly exchange rates and the cumulative translation effect is included in stockholders 2019 equity . the change in functional .