Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(4))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Summary of Significant Accounting Policies - Collaborative Research and Licensing Agreement (Details)	1 Months Ended									3 Months Ended										12 Months Ended
	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Jul. 31, 2016 USD ($)	Jun. 30, 2016 USD ($) item	Sep. 30, 2015 USD ($) item	Dec. 31, 2014 USD ($)	Jul. 31, 2013 USD ($) item	Jan. 31, 2013 USD ($) item	Jun. 30, 2010 USD ($)	Dec. 31, 2017 USD ($) item	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($) item	Mar. 31, 2014 USD ($)	Dec. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2009 USD ($) item	Dec. 31, 2007 item
Collaboration research and licensing agreements
Potential milestone payment										$ 4,448,000,000										$ 4,448,000,000
Revenue recognized										10,941,000	$ 7,090,000	$ 13,340,000	$ 4,340,000	$ 6,440,000	$ 7,821,000	$ 66,007,000	$ 7,252,000			35,711,000	$ 87,520,000	$ 27,762,000
Accounts receivable										1,142,000				8,616,000						1,142,000	8,616,000
Deferred revenue										94,400,000				$ 103,400,000						94,400,000	103,400,000
Novartis
Collaboration research and licensing agreements
Potential milestone payment										2,410,000,000										2,410,000,000
Revenue recognized																				2,300,000	59,700,000
Amgen, Inc.
Collaboration research and licensing agreements
Potential milestone payment										1,647,500,000										1,647,500,000
Revenue recognized																				16,200,000	18,700,000	13,800,000
Novo Nordisk
Collaboration research and licensing agreements
Revenue recognized																					2,700,000	2,900,000
MorphoSys
Collaboration research and licensing agreements
Potential milestone payment										286,500,000										286,500,000
Revenue recognized																				12,500,000
Alexion Pharmaceuticals, Inc.
Collaboration research and licensing agreements
Potential milestone payment										58,000,000										58,000,000
Revenue recognized																				1,000,000	6,000,000	8,500,000
CSL Limited
Collaboration research and licensing agreements
Revenue recognized																				3,500,000		2,500,000
Collaboration And License Agreement \| Novartis
Collaboration research and licensing agreements
Nonrefundable upfront payment			$ 150,000,000
Revenue recognized																				2,300,000	$ 59,700,000
Accounts receivable										1,100,000										1,100,000
Deferred revenue										88,000,000										88,000,000
Collaboration And License Agreement \| Novartis \| Maximum
Collaboration research and licensing agreements
Potential milestone payment										2,400,000,000										$ 2,400,000,000
Collaboration And License Agreement \| Novartis \| Global Discovery Program
Collaboration research and licensing agreements
Number of programs where Company has the right to participate \| item				1
Number of Global discovery programs \| item				4
Percentage of responsibility for development costs				25.00%
Percentage of responsibility for commercialization costs				50.00%
Percentage of profits on net sales of the product				50.00%
Number of bispecific product candidates delivered \| item																					0
Allocation of consideration to deliverables				$ 20,050,000
Collaboration And License Agreement \| Novartis \| Global Discovery Program \| Maximum
Collaboration research and licensing agreements
Number of antibody targets for which bispecific technology applied \| item				4
Collaboration And License Agreement \| Novartis \| FC Licenses
Collaboration research and licensing agreements
Number of bispecific product candidates delivered \| item				4
Allocation of consideration to deliverables				$ 11,300,000
Collaboration And License Agreement \| Novartis \| FC Licenses \| Maximum
Collaboration research and licensing agreements
Number of targets against which non-exclusive license is provided \| item				10
Collaboration And License Agreement \| Novartis \| Bispecific FC Technologies
Collaboration research and licensing agreements
Number of development stage products \| item				2
Number of previously identified products \| item				4
Research license term				5 years
Collaboration And License Agreement \| Novartis \| Bispecific FC Technologies \| XmAb14045
Collaboration research and licensing agreements
Allocation of consideration to deliverables				$ 27,100,000
Collaboration And License Agreement \| Novartis \| Bispecific FC Technologies \| XmAb13676
Collaboration research and licensing agreements
Allocation of consideration to deliverables				$ 31,400,000
Collaboration And License Agreement \| Novartis \| Bispecific FC Technologies \| Maximum
Collaboration research and licensing agreements
Number of antibody targets for which bispecific technology applied \| item				4
Collaboration And License Agreement \| Amgen, Inc. \| Discovery Program
Collaboration research and licensing agreements
Number of bispecific product candidates delivered \| item																				5
Substituted candidates \| item																				1
Collaboration And License Agreement \| Amgen, Inc. \| Discovery Program \| Maximum
Collaboration research and licensing agreements
Number of antibody targets for which bispecific technology applied \| item																		3
Collaboration And License Agreement \| Novo Nordisk
Collaboration research and licensing agreements
Nonrefundable upfront payment																						2,500,000
Research license term						2 years
Revenue recognized																				$ 0	$ 2,700,000	$ 2,900,000
Deferred revenue										0										0
Milestone payment received						$ 1,600,000
Research term of revenue recognized																						2 years
Collaboration And License Agreement \| MorphoSys
Collaboration research and licensing agreements
Nonrefundable upfront payment									$ 13,000,000
Milestone payment	$ 12,500,000
Revenue recognized																				12,500,000	0	$ 0
Deferred revenue										0										0
License Agreement \| Merck Sharp & Dohme Corp.
Collaboration research and licensing agreements
Nonrefundable upfront payment							$ 1,000,000
Revenue recognized																			$ 500,000	100,000	100,000	100,000
Deferred revenue										50,000										50,000
Annual maintenance fees							$ 500,000
Number of compounds \| item							1
Option and license agreement \| Alexion Pharmaceuticals, Inc.
Collaboration research and licensing agreements
Nonrefundable upfront payment								$ 3,000,000
Potential milestone payment								$ 66,500,000
Research license term								5 years
Revenue recognized																				1,000,000	6,000,000	8,500,000
Deferred revenue										83,000										83,000
Number of different target programs \| item								6
Annual maintenance fees								$ 500,000
Annual maintenance fees payable during any extension of research term								2,000,000
Extension fee								$ 1,000,000
Research License and Option Agreement \| Amgen, Inc. \| Bispecific FC Technologies
Collaboration research and licensing agreements
Milestone payment										10,000,000
2009 Research License and Commercialization Agreement \| CSL Limited
Collaboration research and licensing agreements
Nonrefundable upfront payment																								$ 750,000
Potential milestone payment										9,000,000										9,000,000
Milestone payment		$ 3,500,000
Research license term																								5 years
Revenue recognized																				3,500,000	0	2,500,000
Deferred revenue										0										0
Number of commercial options \| item																								5
Number of technologies to which research license is provided \| item																								1
Research Licensee and Collaboration Agreement 2007 Agreement \| Boehringer Ingelheim International GmbH
Collaboration research and licensing agreements
Research license term																									3 years
Revenue recognized																				0	0	0
Deferred revenue										0										0
Milestone payment received																							$ 1,200,000
Number of commercial options \| item																									1
Number of compounds \| item																									2
Research and License Agreement 2015 \| Amgen, Inc.
Collaboration research and licensing agreements
Nonrefundable upfront payment					$ 45,000,000
Potential milestone payment					$ 1,700,000,000
Revenue recognized																				16,200,000	$ 18,750,000	$ 13,750,000
Deferred revenue										$ 6,250,000										6,250,000
Number of different target programs \| item					6
Research and License Agreement 2015 \| Amgen, Inc. \| CD38 Program
Collaboration research and licensing agreements
Allocation of consideration to deliverables																				$ 13,750,000
Research and License Agreement 2015 \| Amgen, Inc. \| Discovery Program
Collaboration research and licensing agreements
Number of previously identified products \| item																				3	3
Research license term																				3 years
Number of bispecific product candidates delivered \| item																					5
Allocation of consideration to deliverables																		$ 6,250,000		$ 6,250,000
Previous targets which bispecific technology will be applied \| item					5					5										5
Additional research term																				1 year
Substituted candidates \| item																	1
Number of delivered discover programs \| item																				0