Related Party Transactions (Details) (Sanofi)	1 Months Ended
Apr. 30, 2012
Sanofi
Related Party Transactions
Shares of common stock purchased by related party in connection with initial public offering	5,217,391

Represents the number of shares of common stock purchased by a related party in connection with the initial public offering.

No definition available.

Name:	mack_RelatedPartyTransactionsSharesPurchasedByRelatedParty
Namespace Prefix:	mack_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration