Deferred Revenue

12 Months Ended

Dec. 31, 2019

Revenue From Contract With Customer [Abstract]

Deferred Revenue

9. Deferred Revenue

Deferred revenue by revenue classification as of December 31, 2019 and 2018 was as follows (in thousands):

	December 31,
	2019		2018
Current deferred revenue
Sequencing	$	12,482	$	11,238
Development		48,512		1,457
Total current deferred revenue		60,994		12,695
Non-current deferred revenue
Sequencing		1,459		516
Development		217,873		188
Total non-current deferred revenue		219,332		704
Total current and non-current deferred revenue	$	280,326	$	13,399

Genentech deferred revenue represents $48.1 million and $216.8 million of the current and non-current development deferred revenue balances, respectively, at December 31, 2019. In general, the current amounts will be recognized as revenue within 12 months and the non-current 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 year ended December 31, 2019 were as follows (in thousands):

Deferred revenue balance at December 31, 2018	$	13,399
Additions to deferred revenue during the period		317,551
Revenue recognized during the period		(50,624	)
Deferred revenue balance at December 31, 2019	$	280,326

As of December 31, 2019, $8.5 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 $1.9 million of sequencing revenue during the year ended December 31, 2019.