Segment Reporting, including Geographic Area Data and Major Customers - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011 Person	Dec. 31, 2010 Person	Dec. 31, 2009 Person
Segment Reporting Information [Line Items]
Entity-wide revenue, major customer, number	1	1	1
Entity-wide revenue, major customer, amount	$ 210.9	$ 221.0	$ 217.7
Percentage of total revenues, by major customer	11.70%	12.90%	12.00%

Amount of revenue generated from a single external customer that accounts for 10 percent or more of an entity's revenues.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 131

-Paragraph 39

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 280

-SubTopic 10

-Section 50

-Paragraph 42

-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e9054-108599

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