Goodwill (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
Jun. 30, 2012	Jun. 30, 2012 Region One	Jun. 30, 2012 Region Two	Jun. 30, 2012 Region Three	Dec. 31, 2011 Region Three	Jun. 30, 2012 Region Four	Dec. 31, 2011 Region Four
Changes in carrying amounts of goodwill
Balance at the beginning of the period	$ 132,417	$ 65,965	$ 8,600	$ 35,275	$ 35,275	$ 22,577	$ 22,577
Contingent payments related to acquisitions	(46)	(46)
Foreign currency translation	20		20
Balance at the end of the period	$ 132,483	$ 66,011	$ 8,620	$ 35,275	$ 35,275	$ 22,577	$ 22,577

Carrying amount as of the balance sheet date, which is the cumulative amount paid and (if applicable) the fair value of any noncontrolling interest in the acquiree, adjusted for any amortization recognized prior to the adoption of any changes in generally accepted accounting principles (as applicable) and for any impairment charges, in excess of the fair value of net assets acquired in one or more business combination transactions.

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

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 7: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

+ Details