Balance at beginning of period

Charged to costs and expenses

Charged to other accounts

Deductions

Balance at end of period

Year Ended December 31, 2020

Allowance for credit losses or doubtful accounts on receivables and contract assets

$

—

$

7

$

—

$

—

$

7

Deferred tax asset valuation allowance

196

(6)

—

190

Year Ended December 31, 2019

Allowance for credit losses or doubtful accounts on receivables and contract assets

$

30

$

16

$

—

$

(46)

$

—

Deferred tax asset valuation allowance

686

(490)

—

196

Year Ended December 31, 2018

Allowance for credit losses or doubtful accounts on receivables and contract assets

$

30

$

—

$

—

$

—

$

30

Deferred tax asset valuation allowance

806

(120)

—

686