20. Segment and Geographic Information

We have two reportable segments organized according to our products and services: Medical Devices and Preservation Services. The Medical Devices segment includes external revenues from product sales of BioGlue, BioFoam, On-X products, JOTEC products, CardioGenesis cardiac laser therapy, PerClot, PhotoFix, HeRO Graft through the second quarter of 2016, and ProCol through the date of the sale of the ProCol product line in the first quarter of 2016. The Preservation Services segment includes external services revenues from the preservation of cardiac and vascular tissues. There are no intersegment revenues.

The primary measure of segment performance, as viewed by our management, is segment gross margin, or net external revenues less cost of products and preservation services. We do not segregate assets by segment; therefore, asset information is excluded from the segment disclosures below.

The following table summarizes revenues, cost of products and preservation services, and gross margins for our operating segments (in thousands):


	2017		2016		2015
Revenues:
Medical devices	$	119,631	$	113,992	$	83,081
Preservation services		70,071		66,388		62,817
Total revenues		189,702		180,380		145,898

Cost of products and preservation services:
Medical devices		29,798		28,033		18,663
Preservation services		31,262		33,448		36,516
Total cost of products and preservation services		61,060		61,481		55,179

Gross margin:
Medical devices		89,833		85,959		64,418
Preservation services		38,809		32,940		26,301
Total gross margin	$	128,642	$	118,899	$	90,719

Net revenues by product for the years ended December 31, 2017, 2016, and 2015 were as follows (in thousands):


	2017		2016		2015
Products:
BioGlue and BioFoam	$	65,939	$	63,461	$	59,332
On-X		37,041		34,232		--
JOTEC		4,136		--		--
CardioGenesis cardiac laser therapy		6,866		7,864		9,419
PerClot		3,533		4,021		4,083
PhotoFix		2,116		1,871		1,396
HeRO Graft		--		2,325		7,546
ProCol		--		218		1,305
Total products		119,631		113,992		83,081

Preservation services:
Cardiac tissue		32,510		29,697		28,059
Vascular tissue		37,561		36,691		34,758
Total preservation services		70,071		66,388		62,817

Total revenues	$	189,702	$	180,380	$	145,898

Net revenues by geographic location attributed to countries based on the location of the customer for the years ended December 31, 2017, 2016, and 2015 were as follows (in thousands):


	2017		2016		2015
U.S.	$	135,102	$	131,727	$	114,978
International		54,600		48,653		30,920
Total revenues	$	189,702	$	180,380	$	145,898

At December 31, 2017 and 2016 60% and 99%, respectively, of our long‑lived assets were held in the U.S., where the corporate headquarters and a portion of our manufacturing facilities are located. At December 31, 2017 $13.3 million of our long-lived assets were located internationally, of which 99% were located in Hechingen, Germany. At December 31, 2017 and 2016 $188.3 million and $78.3 million, respectively, of our goodwill was allocated entirely to our Medical Devices segment.