Workers' Compensation (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Summarizes aggregate workers' compensation reserve activity
Workers' compensation claims liabilities, Beginning balance	$ 70,564	$ 51,193
Add: claims expense accrual:
Current period	12,677	8,163
Prior periods	3,452	0
Total expense accrual	16,129	8,163
Less: claim payments related to:
Current period	426	279
Prior periods	9,055	6,283
Total paid	9,481	6,562
Workers' compensation claims liabilities, Ending balance	77,212	52,794
Incurred but not reported (IBNR)	$ 51,838	$ 38,280

Carrying value as of the balance sheet date of obligations and payables pertaining to claims incurred of a workers compensation nature.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 15

-Subparagraph 5

-Article 9

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.15(5))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.15(a))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 15

-Subparagraph a

-Article 7

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