Deferred Revenue

6 Months Ended

Jun. 30, 2019

Revenue From Contract With Customer [Abstract]

Deferred Revenue

7. Deferred Revenue

Deferred revenue by revenue classification was as follows (in thousands):

	June 30, 2019		December 31, 2018
	(unaudited)
Current deferred revenue
Sequencing	$	14,616	$	11,238
Development		46,578		1,457
Total current deferred revenue		61,194		12,695
Non-current deferred revenue
Sequencing		493		516
Development		240,426		188
Total non-current deferred revenue		240,919		704
Total current and non-current deferred revenue	$	302,113	$	13,399

Genentech deferred revenue represents $45.0 million and $240.2 million of the current and non-current development deferred revenue balances, respectively, at June 30, 2019. In general, the current amounts will be recognized as revenue within 12 months and the long-term amounts will be recognized as revenue over a period of approximately seven to eight years. This period of time represents an estimate of the research and development period to develop cellular therapies in oncology, which may be reduced or increased based on the various development activities.

Changes in deferred revenue during the six months ended June 30, 2019 were as follows (in thousands):

Deferred revenue balance at December 31, 2018	$	13,399
Additions to deferred revenue during the period (unaudited)		308,055
Revenue recognized during the period (unaudited)		(19,341	)
Deferred revenue balance at June 30, 2019 (unaudited)	$	302,113

As of June 30, 2019, $4.4 million was recognized that was included in the deferred revenue balance at December 31, 2018. As a result of cancelled customer sequencing contracts, we recognized $0.8 million of sequencing revenue during the six months ended June 30, 2019.