Changes in Goodwill (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended		9 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Mideast Group	Jun. 30, 2012 Mideast Group	Sep. 30, 2012 Southeast Group	Jun. 30, 2012 Southeast Group	Sep. 30, 2012 West Group	Sep. 30, 2012 West Group
Goodwill
Balance at beginning of period	$ 618,874	$ 616,671	$ 639,039	$ 122,052	$ 112,823	$ 72,073	$ 81,302	$ 424,749	$ 422,546
Adjustments to purchase price allocations	(2,888)	(685)						(2,888)	(685)
District reorganization				(9,229)		9,229
Balance at end of period	$ 615,986	$ 615,986	$ 639,039	$ 112,823	$ 112,823	$ 81,302	$ 81,302	$ 421,861	$ 421,861

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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