Note 13. Segment, Geographic, Product and Significant Customer Information

The Company has one operating segment, which is the sale, design, manufacture, marketing and support of optical critical dimension and thin film systems. The following tables summarize total net revenues and long-lived assets (excluding intangible assets) attributed to significant countries (in thousands):

	Three Months Ended
	March 31, 2018		April 1, 2017
Total net revenues^(1):
South Korea	$	37,818	$	18,619
Japan		13,379		3,353
United States		6,738		13,573
China		8,042		6,687
Taiwan		1,060		11,833
Singapore		12,155		1,491
Other		3,121		3,758
Total net revenues	$	82,313	$	59,314

	March 31, 2018		December 30, 2017
Long-lived tangible assets:
United States	$	42,473	$	43,427
International		1,322		1,383
Total long-lived tangible assets	$	43,795	$	44,810

With respect to customer concentration, Samsung Electronics Co. Ltd, SK Hynix, Micron Technology, Inc. and Toshiba Corporation each accounted for more than 10% of total sales for the three months ended March 31, 2018. Samsung Electronics Co. Ltd, SK Hynix, Taiwan Semiconductor Manufacturing Company Limited and Intel Corporation each accounted for more than 10% of total sales for the three months ended April 1, 2017.

With respect to accounts receivable concentration, Samsung Electronics Co. Ltd, SK Hynix, Micron Technology, Inc. and Toshiba Corporation each accounted for more than 10% of total accounts receivable at March 31, 2018 and Samsung Electronics Co. Ltd, Micron Technology, Inc, and Toshiba Corporation each accounted for more than 10% of total accounts receivable at December 30, 2017.