On January 1, 2020, we adopted ASU 2016-13 Financial Instruments – Credit Losses (Topic 326) Measurement of Credit Losses on Financial Instruments, which introduces a new model to measure all expected credit losses for financial instruments held at the reporting date based on historical experience, current conditions and reasonable and supportable forecasts. Our customers are primarily oil and natural gas exploration and production companies, which are collectively exposed to oil and natural gas commodity price risk. Our customers require services from us at various stages of the exploration and production process. Accordingly, we have aggregated our trade receivables by segment. Any customers that have experienced a deterioration in credit quality are removed from the pool and evaluated individually. We utilized an accounts receivable aging schedule and historical credit loss information to estimate expected credit losses. Due to the significant decline in crude oil prices during the quarter ended March 31, 2020 and its related impact to our customers, we increased our historical credit loss rates used to determine our March 31, 2020 allowance for credit losses in the first quarter of 2020. We continued to monitor and evaluate our expected credit losses using these increased credit loss rates throughout the remainder of 2020.

The adoption of the new accounting standard did not have a material impact on our consolidated financial statements and did not result in a transition adjustment to retained earnings.

The allowance for credit losses related to accounts receivable as of December 31, 2020, and changes for the quarters ended March 31, June 30, September 30 and December 31, 2020 are as follows (in thousands):

Balance at December 31, 2019	$	6,516
Provision for expected credit losses		1,055
Balance at March 31, 2020		7,571
Provision for expected credit losses		4,551
Balance at June 30, 2020		12,122
Write-offs		(1,126	)
Balance at September 30, 2020		10,996
Write-offs		(154	)
Balance at December 31, 2020	$	10,842