Reconciliation of Segment Income from Operations to Income before Income Taxes (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment income from operations	$ 65,762	$ 53,642	[1]
Interest and other debt expense	15,588	13,940
Income before income taxes	$ 50,174	$ 39,702

[1] Income from operations for corporate includes costs attributable to announced acquisitions of $1.8 million.