Revenues

6 Months Ended

Jun. 30, 2019

Revenue from Contract with Customer [Abstract]

Revenues

Revenues

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Xyrem	$	413,212	$	356,008	$	781,529	$	672,785
Erwinaze/Erwinase	27,622		58,713		88,521		109,340
Defitelio/defibrotide	46,055		40,498		87,555		75,559
Vyxeos	31,362		27,951		60,305		54,179
Other	5,172		12,925		8,844		25,079
Product sales, net	523,423		496,095		1,026,754		936,942
Royalties and contract revenues	10,710		4,384		15,565		8,150
Total revenues	$	534,133	$	500,479	$	1,042,319	$	945,092

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
United States	$	480,932	$	455,359	$	943,794	$	861,046
Europe	36,518		35,018		71,919		63,349
All other	16,683		10,102		26,606		20,697
Total revenues	$	534,133	$	500,479	$	1,042,319	$	945,092

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Express Scripts	77	%	71	%	75	%	71	%
McKesson	12	%	20	%	15	%	20	%

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 June 30, 2019 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 $1.2 million and $3.1 million during the three and six months ended June 30, 2019, respectively, relating to these upfront payments. The deferred revenue balances are being recognized over an average of four years representing the period over which 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 six months ended June 30, 2019 (in thousands): 

	Contract Liabilities
Balance as of December 31, 2018	$	14,995
Amount recognized within royalties and contract revenues	(3,054		)
Balance as of June 30, 2019	$	11,941