We operate in one business segment which focuses on applying our technology platforms 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 customers in the pharmaceutical and biotechnology industries. Revenue from BMS represented 89% of our revenue for the year ended December 31, 2018. Revenue from 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 by geographic area is based on the headquarters or shipping locations of our partners. The following table sets forth revenue by geographic area (in thousands):

	Year Ended December 31,
	2018		2017		2016
United States	$	1,090,794	$	190,810	$	39,147
Europe		102,529		116,901		126,289
Total revenue	$	1,193,323	$	307,711	$	165,436

At December 31, 2018, $42.9 million, or approximately 88%, of the net book value of our property, plant and equipment was located in the United States and $5.9 million, or approximately 12%, was located in India. 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.