Summary of Significant Accounting Policies and Other Information (Tables)

9 Months Ended

Sep. 30, 2021

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedules of Concentration of Risk, by Risk Factor

The following table presents customers individually accounting for more than 10% of the Company’s net sales:

	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
	2021		2020		2021		2020
Customer A	20	%	17	%	21	%	10	%
Customer B	17	%	11	%	16	%	14	%
Customer C	**		11	%	**		11	%

The following table presents customers individually accounting for more than 10% of the Company’s accounts receivable:

	As of September 30, 2021		As of December 31, 2020
Customer B	26	%	16	%
Customer C	14	%	**
Customer D	**		22	%

The following table presents suppliers individually accounting for more than 10% of the Company’s purchases:

	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
	2021		2020		2021		2020
Supplier A	11	%	38	%	**		25	%
Supplier B	10	%	**		13	%	**

**Less than 10% of the total

Schedule of Inventory, Current

Inventories consisted of the following:

(in thousands) Inventories	As of September 30, 2021		As of December 31, 2020
Raw materials *	$	126,225	$	89,684
Work in process	2,850		2,482
Finished goods	19,115		19,375
Total inventories	148,190		111,541
Inventory allowance	(3,376)		(3,328)
Inventories, net	$	144,814	$	108,213

*As of September 30, 2021 and December 31, 2020, raw materials included $12.0 million and $36.6 million, respectively, of 6.0L engines that were purchased for a customer under a long-term supply agreement. See Note 2. Revenue for additional information related to contract liabilities and remaining performance obligations related to these engines.

Activity in the Company’s inventory allowance was as follows:

(in thousands)	For the Nine Months Ended September 30,
Inventory Allowance	2021		2020
Balance at beginning of period	$	3,328	$	2,964
Charged to expense	607		1,272
Write-offs	(559)		(1,012)
Balance at end of period	$	3,376	$	3,224

Schedule of Other Accrued Liabilities

Other accrued liabilities consisted of the following:

(in thousands) Other Accrued Liabilities	As of September 30, 2021		As of December 31, 2020
Accrued product warranty	$	15,247	$	14,928
Litigation reserves *	1,707		3,128
Contract liabilities	17,267		47,960
Accrued compensation and benefits	3,862		3,124
Operating lease liabilities	3,868		3,793
Accrued interest expense	254		895
Other	8,478		3,791
Total	$	50,683	$	77,619

*As of September 30, 2021 and December 31, 2020 litigation reserves related to various ongoing legal matters including associated legal fees as well as accrued indemnification costs related to former officers and employees of the Company. See Note 9. Commitments and Contingencies for additional information.

Schedule of Accrued Product Warranty

Accrued product warranty activities are presented below:

(in thousands)	For the Nine Months Ended September 30,
Accrued Product Warranty	2021		2020
Balance at beginning of period	$	31,542	$	25,501
Current year provision *	14,135		13,949
Changes in estimates for preexisting warranties **	3,750		8,756
Payments made during the period	(19,244)		(15,357)
Balance at end of period	30,183		32,849
Less: current portion	15,247		16,210
Noncurrent accrued product warranty	$	14,936	$	16,639

*Warranty costs, net of supplier recoveries, were $14.8 million and $18.2 million for the nine months ended September 30, 2021 and 2020, respectively. Supplier recoveries were $3.3 million and $4.6 million for the nine months ended September 30, 2021 and 2020, respectively.

**Changes in estimates for preexisting warranties reflect changes in the Company’s estimate of warranty costs for products sold in prior periods. Such adjustments typically occur when claims experience deviates from historical and expected trends. The Company recorded charges for changes in estimates of preexisting warranties of $3.8 million, or $0.16 per diluted share, for the nine months ended September 30, 2021, and charges of $8.8 million, or $0.38 per diluted share, for the nine months ended September 30, 2020, respectively.