Summary of Significant Accounting Policies (Details 3)	3 Months Ended
Mar. 31, 2013 item
Summary of Significant Accounting Policies
Number of issues with limited investment as per investment policy	1

Represents the number of issues in which entity will limit its investment as per investment policy so as to reduce the credit risk.

No definition available.

Name:	mack_NumberOfIssuesToLimitInvestmentAmountAsPerInvestmentPolicy
Namespace Prefix:	mack_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration