Merger (Details) - USD ($) $ / shares in Units, $ in Thousands			6 Months Ended	12 Months Ended			60 Months Ended
	Jul. 15, 2014	Jul. 15, 2014	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015
Acquisition-date fair value of the consideration transferred
Stock-based compensation expense				$ 3,470	$ 1,719
Estimated fair values of the assets acquired and liabilities assumed at the date of acquisition:
Goodwill			$ 16,363	26,361	16,363		$ 26,361
Deferred tax liabilities			0	(757)	0		(757)
Supplemental unaudited pro forma information:
Net loss				(52,188)	(41,844)		$ (138,759)
Zalicus
Merger
Number of shares of acquiree received for each share of acquirer exchanged		0.13259
Aggregate number of acquiree shares received for acquirer shares		10,288,180
Number of acquiree shares received for future issuance upon exercise of stock options		1,152,042
Number of acquiree shares received for future issuance upon exercise of warrants		21,996
Acquisition-date fair value of the consideration transferred
Number of Public Epirus Common Stock owned by Zalicus stockholders (1)		2,635,871
Multiplied by the price per share of Public Epirus Common Stock (2) (in dollars per share)	$ 11.80	$ 11.80
Fair value of shares of Public Epirus Common Stock owned by Zalicus stockholders		$ 31,104
Acquisition-date fair value of assumed Zalicus equity awards attributable to precombination		220
Total consideration transferred		31,324
Amount of fractional shares resulting from Reverse Stock Split included as consideration		$ 1
Share price (in dollars per share)	$ 11.80	$ 11.80
Volatility rate		66.02%
Risk-free interest rate		1.91%
Estimated fair values of the assets acquired and liabilities assumed at the date of acquisition:
Cash and cash equivalents	$ 13,756	$ 13,756
In-process research and development	5,500	5,500
Goodwill	14,127	14,127
Restricted cash	1,850	1,850
Other assets	253	253
Total assets acquired	35,486	35,486
Accounts payable	(1,584)	(1,584)
Accrued expenses	(381)	(381)
Other current liabilities	(376)	(376)
Other liabilities	(391)	(391)
Deferred tax liabilities	(1,430)	(1,430)
Total liabilities assumed	(4,162)	(4,162)
Total net assets acquired	$ 31,324	$ 31,324
Goodwill adjustment				736
Operating loss from date of acquisition included in financial statements			$ (25)
Business Combination, Acquisition Related Costs					5,779
Supplemental unaudited pro forma information:
Total revenues, net				2,739	14,731
Net loss				$ (32,410)	(69,630)
Zalicus | Transaction Costs
Supplemental unaudited pro forma information:
Net loss					8,673
Zalicus | stock-based compensation expense
Supplemental unaudited pro forma information:
Net loss					355
Zalicus | severance agreements
Supplemental unaudited pro forma information:
Net loss					1,980
Zalicus | other expense related to the change in the fair values of liability-classified warrants
Supplemental unaudited pro forma information:
Net loss					$ 222	$ 789
Zalicus | In Process Research and Development
Estimated fair values of the assets acquired and liabilities assumed at the date of acquisition:
Discount rate (as a percent)		13.10%
Zalicus | Minimum
Acquisition-date fair value of the consideration transferred
Exercise price (in dollars per share)	$ 14.70	$ 14.70
Expected term	1 month 6 days
Zalicus | Maximum
Acquisition-date fair value of the consideration transferred
Exercise price (in dollars per share)	$ 591.00	$ 591.00
Expected term	6 years
Zalicus | Common stock
Acquisition-date fair value of the consideration transferred
Number of Public Epirus Common Stock owned by Zalicus stockholders (1)		2,610,871
Zalicus | Restricted stock units vested upon closing of business combination
Acquisition-date fair value of the consideration transferred
Number of Public Epirus Common Stock owned by Zalicus stockholders (1)		25,000
Preliminary | Zalicus
Estimated fair values of the assets acquired and liabilities assumed at the date of acquisition:
Deferred tax liabilities	$ (2,166)	$ (2,166)