Fair Value of Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Schedule of Fair Value Measurements at Reporting Date

(in thousands)	As of December 31, 2019
	Carrying Value		Fair Value
			Level 1		Level 2		Level 3
Wells Fargo Credit Agreement	$	39,527	$	—	$	39,527	$	—
Unsecured Senior Notes	54,765		—		—		54,600

(in thousands)	As of December 31, 2018
	Carrying Value		Fair Value
			Level 1		Level 2		Level 3
Wells Fargo Credit Agreement	$	54,613	$	—	$	54,613	$	—
Unsecured Senior Notes	54,712		—		—		52,700

(in thousands)	As of December 31, 2018
	Carrying Value		Fair Value
			Level 1		Level 2		Level 3
Warrant liability	$	35,100	$	—	$	—	$	35,100

Summary of Change in the Estimated Fair Value of Private Placement Warrants

The following table summarizes changes in the estimated fair value of the Company’s warrant liability:

(in thousands)	As of December 31,
	2019			2018
Balance at beginning of year	$	35,100		$	24,700
Change in value of warrants *	1,352			10,400
Settlement of warrants	(36,452		)	—
Balance at end of year	$	—		$	35,100

* The change in value of the warrant liability for each year is presented in Loss from change in value and exercise of warrants in the Company’s Consolidated Statements of Operations. The change in value for the year ended December 31, 2019 includes the impact of Weichai exercising the warrant in April 2019.

Schedule of Inputs of the Black-Scholes Option Pricing Model

The inputs of the Black-Scholes option pricing model were as follows:

Assumptions	As of December 31,
	2018
Market value of the Common Stock	$	9.25
Exercise price	varies
Risk-free interest rate	2.6		%
Estimated price volatility	55.0		%
Contractual term	0.5 years