2. TRADE ACCOUNTS RECEIVABLE

The Company's receivables result primarily from the sale of transportation and logistics services. The Company performs ongoing credit evaluations of its customers and generally does not require collateral for accounts receivable. Accounts receivable which consist of both billed and unbilled receivables are presented net of an allowance for doubtful accounts. Accounts outstanding longer than contractual payment terms are considered past due and are reviewed individually for collectibility. Accounts receivable balances consist of the following components as of December 31, 2012 and 2011:

	2012			2011
	(in thousands)

Billed	$	44,374		$	44,370
Unbilled		6,800			5,723
Allowance for doubtful accounts		(1,157	)		(2,074	)

Total accounts receivable—net	$	50,017		$	48,019

An analysis of changes in the allowance for doubtful accounts for the years ended December 31, 2012, 2011 and 2010 follows:

	2012			2011			2010
	(in thousands)

Balance—beginning of year	$	2,074		$	2,418		$	2,660
Provision for bad debts		(285	)		22			529
Charge-offs		(632	)		(565	)		(1,100	)
Recoveries		-			199			329
Balance—end of year	$	1,157		$	2,074		$	2,418