Merger (Details) (USD $) In Thousands, except Share data, unless otherwise specified	0 Months Ended	3 Months Ended	12 Months Ended
	Jul. 15, 2014	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Jul. 15, 2014	Jul. 14, 2014
Acquisition-date fair value of the consideration transferred
Stock-based compensation expense			$ 1,719	$ 140
Estimated fair values of the assets acquired and liabilities assumed at the date of acquisition:
Goodwill			16,363	1,499
Supplemental unaudited pro forma information as if acquisition had occurred on January 1, 2013:
Net loss			(41,844)	(20,795)
Zalicus
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 services (3)	220
Total consideration transferred	31,324
Amount of fractional shares resulting from Reverse Stock Split included as consideration	1
Stock-based compensation expense		355
Exercise price (in dollars per share)	$ 591.00				$ 591.00
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
In-process research and development						5,500
Goodwill						14,864
Restricted cash						1,850
Other assets						253
Total assets acquired						36,223
Accounts payable						(1,584)
Accrued expenses						(381)
Other current liabilities						(376)
Other liabilities						(391)
Deferred tax liabilities						(2,166)
Total liabilities assumed						(4,899)
Total net assets acquired						31,324
Other liabilities of accrued expenses and other liabilities relates to a sublease liability	376
Effective tax rate	39.39%
Operating loss from date of acquisition included in financial statements		25
Business Combination, Acquisition Related Costs			5,779
Supplemental unaudited pro forma information as if acquisition had occurred on January 1, 2013:
Total revenues, net			2,739	14,731
Net loss			(32,410)	(69,630)
Zalicus | Transaction Costs
Supplemental unaudited pro forma information as if acquisition had occurred on January 1, 2013:
Net loss			8,673
Zalicus | stock-based compensation expense
Supplemental unaudited pro forma information as if acquisition had occurred on January 1, 2013:
Net loss			355
Zalicus | severance agreements
Supplemental unaudited pro forma information as if acquisition had occurred on January 1, 2013:
Net loss			1,980
Zalicus | other expense related to the change in the fair values of liability-classified warrants
Supplemental unaudited pro forma information as if acquisition had occurred on January 1, 2013:
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
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 | RestrictedStockUnitsVestedUponClosingOfBusinessCombinationMember
Acquisition-date fair value of the consideration transferred
Number of Public Epirus Common Stock owned by Zalicus stockholders (1)	25,000
Zalicus | Common Class A
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