Summary of Significant Accounting Principles - Additional Information (Detail)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017 USD ($) Customer	Jun. 30, 2016 USD ($) Customer	Jun. 30, 2017 USD ($) Customer	Jun. 30, 2016 USD ($) Customer	Dec. 31, 2016 USD ($) Customer
Summary Of Significant Accounting Policies [Line Items]
Equity method investments	$ 0		$ 0		$ 0
Guarantee or other funding obligations under equity method investment	0		0
Losses from equity method investment	0	$ 0	0	$ 0
Note payable - related party	$ 1,298,000		$ 1,298,000		1,195,000
Number of customers with revenues greater than 10% | Customer	0	0	0	0
Number of customers with accounts receivable greater than 10% | Customer			0
Inventories finished goods and purchased parts	$ 24,002,000		$ 24,002,000		14,531,000
Inventories raw materials	5,679,000		$ 5,679,000		$ 8,686,000
Warranty period			1 year
Caterpillar Inc. [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of customers with accounts receivable greater than 10% | Customer					1
Accounts Receivable | Customer Concentration Risk | Caterpillar Inc. [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration risk percentage					10.50%
8.0% Senior Secured Notes due 2024 [Member]
Summary Of Significant Accounting Policies [Line Items]
Carrying amount of debt	250,000,000		$ 250,000,000
Fair value of senior secured notes	$ 263,000,000		$ 263,000,000