Investments and Fair Value Measurements - Summary of Changes in Contingent Liability for Self-Insurance (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
Jun. 30, 2013	Dec. 31, 2012
Statement Of Financial Position [Abstract]
Beginning Balance, Fair value of self-insurance liability	$ 1,375	$ 1,640
Additions to reserve	5,920	12,440
Employee contributions	1,154	2,340
Less: insurance claims, stop loss premium, and administrative fees paid	(6,891)	(15,045)
Ending Balance, Fair value of self-insurance liability	$ 1,558	$ 1,375

Carrying amount (including both current and noncurrent portions) of accrued known and estimated losses incurred as of the balance sheet date for which no insurance coverage exists, and for which a claim has been made or is probable of being asserted, typically arising from workmen's compensation-type of incidents and personal injury to nonemployees from accidents on the entity's property.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.24)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_SelfInsuranceReserve
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant