7. Segment Information and Concentration of Business Risk

We have two reportable segments Ionis Core and Akcea Therapeutics. At December 31, 2018, we owned approximately 75 percent of Akcea. Segment income (loss) from operations includes revenue less operating expenses attributable to each segment.

In our Ionis Core segment we are exploiting our antisense technology to generate a broad pipeline of first-in-class and/or best-in-class medicines for us and our partners. Our Ionis Core segment generates revenue from a multifaceted partnering strategy.

Akcea is a biopharmaceutical company focused on developing and commercializing medicines to treat patients with rare and serious diseases.

The following tables show our segment revenue and income (loss) from operations for 2018, 2017 and 2016 (in thousands), respectively.

2018	Ionis Core		Akcea Therapeutics			Elimination of Intercompany Activity			Total
Revenue:
Commercial revenue:
SPINRAZA royalties	$	237,930	$	—		$	—		$	237,930
TEGSEDI product sales, net		—		2,237			—			2,237
Licensing and other royalty revenue		2,755		12,000			—			14,755
Total commercial revenue		240,685		14,237			—			254,922
R&D revenue under collaborative agreements		401,259		50,630			(107,137	)		344,752
Total segment revenue	$	641,944	$	64,867		$	(107,137	)	$	599,674
Total operating expenses	$	380,212	$	295,683		$	(14,849	)	$	661,046
Income (loss) from operations	$	261,732	$	(230,816	)	$	(92,288	)	$	(61,372	)

2017 (as revised)	Ionis Core		Akcea Therapeutics			Elimination of Intercompany Activity			Total
Revenue:
Commercial revenue:
SPINRAZA royalties	$	112,540	$	—		$	—		$	112,540
Licensing and other royalty revenue		7,474		—			—			7,474
Total commercial revenue		120,014		—			—			120,014
R&D revenue under collaborative agreements		405,171		43,401			(54,407	)		394,165
Total segment revenue	$	525,185	$	43,401		$	(54,407	)	$	514,179
Total operating expenses	$	373,788	$	163,871		$	(54,527	)	$	483,132
Income (loss) from operations	$	151,397	$	(120,470	)	$	120		$	31,047

2016 (as revised)	Ionis Core		Akcea Therapeutics			Elimination of Intercompany Activity			Total
Revenue:
Commercial revenue:
SPINRAZA royalties	$	883	$	—		$	—		$	883
Licensing and other royalty revenue		21,884		—			—			21,884
Total commercial revenue		22,767		—			—			22,767
R&D revenue under collaborative agreements		362,657		—			(12,648	)		350,009
Total segment revenue	$	385,424	$	—		$	(12,648	)	$	372,776
Total operating expenses	$	322,192	$	83,512		$	(12,768	)	$	392,936
Income (loss) from operations	$	63,232	$	(83,512	)	$	120		$	(20,160	)

The following table shows our total assets by segment at December 31, 2018 and 2017 (in thousands), respectively.

Total Assets	Ionis Core		Akcea Therapeutics		Elimination of Intercompany Activity			Total
December 31, 2018	$	2,975,491	$	365,261	$	(672,968	)	$	2,667,784
December 31, 2017 (as revised)	$	1,342,578	$	268,804	$	(288,608	)	$	1,322,774

Contracts receivables at December 31, 2018 and December 31, 2017 were comprised of approximately 99 percent and 84 percent for each year from four and two significant partners, respectively.