Revenues

The following table presents a summary of total revenues (in thousands):



	Year Ended December 31,
	2018		2017		2016
Xyrem	$	1,404,866	$	1,186,699	$	1,107,616
Erwinaze/Erwinase	174,739		197,340		200,678
Defitelio/defibrotide	149,448		133,650		108,952
Vyxeos	100,835		33,790		—
Prialt	20,839		27,361		29,120
Other	18,746		22,559		30,895
Product sales, net	1,869,473		1,601,399		1,477,261
Royalties and contract revenues	21,449		17,294		10,712
Total revenues	$	1,890,922	$	1,618,693	$	1,487,973

The following table presents a summary of total revenues attributed to geographic sources (in thousands):



	Year Ended December 31,
	2018		2017		2016
United States	$	1,727,576	$	1,463,457	$	1,355,921
Europe	125,911		125,624		108,301
All other	37,435		29,612		23,751
Total revenues	$	1,890,922	$	1,618,693	$	1,487,973

The following table presents a summary of the percentage of total revenues from customers that represented more than 10% of our total revenues:



	Year Ended December 31,
	2018		2017		2016
Express Scripts	74	%	73	%	74	%
McKesson	17	%	16	%	15	%

Financing and payment

Our payment terms vary by the type and location of our customer but payment is generally required in a term ranging from 30 to 45 days.

Contract Liabilities - Deferred Revenue

The deferred revenue balance as of December 31, 2018 primarily related to deferred upfront fees received from Nippon Shinyaku Co., Ltd., or Nippon Shinyaku, in connection with two license, development and commercialization agreements granting Nippon Shinyaku exclusive rights to develop and commercialize each of Defitelio and Vyxeos in Japan. We recognized contract revenues of $7.5 million in 2018 relating to these upfront payments. The deferred revenue balances are being recognized over an average of four years representing the period we expect to perform our research and developments obligations under each agreement.

The following table presents a reconciliation of our beginning and ending balances in contract liabilities from contracts with customers for the year ended December 31, 2018 (in thousands):



	Contract Liabilities
Balance as of December 31, 2017	$	24,733
Effect of adoption of ASU 2014-09	(2,240		)
Amount recognized within royalties and contract revenues	(7,498		)
Balance as of December 31, 2018	$	14,995