Nature of operations, basis of presentation and recently issues accounting pronouncements - Additional Information (Detail)	3 Months Ended
Mar. 31, 2015 Segment
Organization Consolidation Basis Of Presentation Business Description And Accounting Policies [Abstract]
Number Of Reporting Units	4us-gaap_NumberOfReportingUnits

Number of reporting units tested for impairment of goodwill. A reporting unit is an operating segment or one level below an operating segment.

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Reporting Unit

-URI http://asc.fasb.org/extlink&oid=6523643

Name:	us-gaap_NumberOfReportingUnits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration