Deferred Revenue (Tables)

3 Months Ended

Mar. 31, 2019

Deferred Revenue Disclosure [Abstract]

Summary of Changes in Deferred Revenue

The following table presents the changes in deferred revenue for the periods presented (in thousands):

	Three Months Ended March 31,
	2019			2018
Balance at beginning of period	$	834		$	1,215
Deferral of revenue		236			13
Recognition of deferred revenue		(69	)		(486	)
Balance at end of period	$	1,001		$	742