Summary of Significant Accounting Principles - Additional Information (Detail)	3 Months Ended		12 Months Ended
	Mar. 31, 2017 USD ($) Customer	Mar. 31, 2016 USD ($) Customer	Dec. 31, 2016 USD ($) Customer
Summary Of Significant Accounting Policies [Line Items]
Equity method investments	$ 0		$ 0
Guarantee or other funding obligations under equity method investment	0
Losses from equity method investment	$ 0	$ 0
Number of customers with revenues greater than 10% | Customer	0	0
Number of customers with accounts receivable greater than 10% | Customer	0
Inventories finished goods and purchased parts	$ 18,030,000		14,531,000
Inventories raw materials	$ 5,371,000		$ 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%