Segment Reporting - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Sales Information [Line Items]
Number of operating business segment	1nktr_NumberOfOperatingBusinessSegment
Number of components within business segment	2
Property and equipment, net	70,368us-gaap_PropertyPlantAndEquipmentNet	66,974us-gaap_PropertyPlantAndEquipmentNet
United States [Member]
Sales Information [Line Items]
Property and equipment, net	63,700	57,300
Percentage of net book value of property and equipment	90.00%	88.00%
India [Member]
Sales Information [Line Items]
Property and equipment, net	6,700	7,700
Percentage of net book value of property and equipment	10.00%	12.00%
Revenue [Member] \| AstraZeneca [Member]
Sales Information [Line Items]
Percentage revenue from clients	52.00%	17.00%
Revenue [Member] \| UCB [Member]
Sales Information [Line Items]
Percentage revenue from clients	16.00%	21.00%	30.00%
Revenue [Member] \| Roche [Member]
Sales Information [Line Items]
Percentage revenue from clients	11.00%	28.00%	23.00%
Revenue [Member] \| Bayer [Member]
Sales Information [Line Items]
Percentage revenue from clients		10.00%
Revenue [Member] \| Affymax, Inc. [Member]
Sales Information [Line Items]
Percentage revenue from clients			11.00%