Segment Reporting

12 Months Ended

Dec. 31, 2017

Note 13 — Segment Reporting

We operate in one business segment which focuses on applying our technology platforms to improve the performance of established drugs and to develop novel drug candidates. Our business offerings have similar economics and other characteristics, including the nature of products and manufacturing processes, types of customers, distribution methods and regulatory environment. We are comprehensively managed as one business segment by our Chief Executive Officer.

Our revenue is derived primarily from clients in the pharmaceutical and biotechnology industries. Lilly and UCB represented 42% and 12% of our revenue, respectively, for the year ended December 31, 2017. Revenue from AstraZeneca, UCB, Ophthotech and Roche represented 29%, 21%, 19% and 11% of our revenue, respectively, for the year ended December 31, 2016. Revenue from AstraZeneca and UCB represented 57% and 13% of our revenue, respectively, for the year ended December 31, 2015 .

Revenue by geographic area is based on the locations of our partners. The following table sets forth revenue by geographic area (in thousands):

	Year Ended December 31,
	2017		2016		2015
United States	$	190,810	$	39,147	$	40,400
Europe		116,901		126,289		190,384
Total revenue	$	307,711	$	165,436	$	230,784

At December 31, 2017, $41.7 million, or approximately 88%, of the net book value of our property, plant and equipment was located in the United States and $5.8 million, or approximately 12%, was located in India. At December 31, 2016, $48.8 million, or approximately 74%, of the net book value of our property, plant and equipment was located in the United States, $10.4 million, or approximately 16% was located at contract manufacturers in Germany and the Netherlands, $5.6 million, or approximately 9%, was located in India, and $0.8 million or approximately 1%, was located in other countries.