Results of Operations (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended
Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 2013 Acquisitions [Member]	Jun. 30, 2012 2013 Acquisitions [Member]	Jun. 30, 2013 2013 Acquisitions [Member]	Jun. 30, 2012 2013 Acquisitions [Member]	Jun. 30, 2012 2012 Acquisitions [Member]	Jun. 30, 2011 2012 Acquisitions [Member]	Jun. 30, 2012 2012 Acquisitions [Member]	Jun. 30, 2011 2012 Acquisitions [Member]
Business Acquisition, Pro Forma Information [Line Items]
Total revenues					$ 326,753	$ 292,242	$ 663,460	$ 596,931	$ 291,763	$ 277,522	$ 599,965	$ 570,176
Income before income taxes					86,506	71,528	186,503	154,953	71,473	70,022	156,202	155,203
Net income					$ 52,179	$ 42,700	$ 112,616	$ 92,511	$ 42,667	$ 42,189	$ 93,257	$ 93,622
Net income per share:
Basic					$ 0.36	$ 0.30	$ 0.78	$ 0.65	$ 0.30	$ 0.30	$ 0.65	$ 0.66
Diluted					$ 0.36	$ 0.29	$ 0.77	$ 0.63	$ 0.29	$ 0.29	$ 0.64	$ 0.64
Weighted average number of shares outstanding:
Basic	140,836	139,086	140,816	139,044	140,836	139,086	140,816	139,044	139,086	138,379	139,044	138,365
Diluted	143,021	141,828	142,938	141,664	143,021	141,828	142,938	141,664	141,828	139,942	141,664	140,950

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The pro forma income from continuing operations before changes in accounting and extraordinary items, net of tax effect per basic share of common stock for a period as if the business combination or combinations had been completed at the beginning of a period.

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