Commitments And Contingencies - Additional Information (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended
Feb. 28, 2014 sqft	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Commitments and Contingencies Disclosure [Abstract]
Total rent expense, net of sublease income		$ 7.9us-gaap_OperatingLeasesRentExpenseNet	$ 9.7us-gaap_OperatingLeasesRentExpenseNet	$ 12.3us-gaap_OperatingLeasesRentExpenseNet
Sublease income				$ 0.7
Square Feet of Office Space Vacated	47,592mso_SquareFeetofOfficeSpaceVacated

The total amount of sublease rental income recognized during the period that reduces the entity's rent expense incurred under operating leases.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 10

-Section 55

-Paragraph 40

-Subparagraph (Note 3)

-URI http://asc.fasb.org/extlink&oid=6584154&loc=d3e38371-112697

Name:	us-gaap_OperatingLeasesRentExpenseSubleaseRentals1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration