Schedule of Calculation of Numerator and Denominator in Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 57,277	$ 51,738
Weighted average shares and assumed conversions	117,768	116,960
BASIC EARNINGS PER SHARE	$ 0.49	$ 0.45
DILUTED EARNINGS PER SHARE	$ 0.49	$ 0.44
Basic Earnings Per Share
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	57,277	51,738
Weighted average common shares outstanding, basic	116,634	115,773
Diluted Earnings Per Share
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 57,277	$ 51,738
Weighted average common shares outstanding, diluted	116,634	115,773
Stock options
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Effect of dilutive securities	869	963
Restricted stock based compensation
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Effect of dilutive securities	265	224