Retirement Benefits - Additional information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2013 Person	Dec. 31, 2012 Person	Dec. 31, 2011 Person
Disclosure Retirement Benefits Additional Information [Abstract]
Matched employee contribution	100.00%
Employee contribution on gross wages	7.00%	6.00%	6.00%
Number of employee participating in plan	585	661	625
Contribution expense	$ 3,621	$ 2,809	$ 2,390

The amount of the cost recognized during the period for defined contribution plans.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 70

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942

Name:	us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration