Schedule of Calculation of Numerator and Denominator in Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income, Basic									$ 159,207	$ 178,040	$ 219,919
Net income, Diluted									$ 159,207	$ 178,040	$ 219,919
Weighted average common shares outstanding, Basic									118,544	118,084	117,384
Weighted average common shares outstanding, Basic									118,544	118,084	117,384
Weighted average shares and assumed conversions									118,716	118,465	117,791
BASIC EARNINGS PER SHARE	$ 0.35	$ 0.35	$ 0.33	$ 0.32	$ 0.35	$ 0.35	$ 0.38	$ 0.42	$ 1.34	$ 1.51	$ 1.87
DILUTED EARNINGS PER SHARE	$ 0.35	$ 0.34	$ 0.33	$ 0.32	$ 0.35	$ 0.35	$ 0.38	$ 0.42	$ 1.34	$ 1.50	$ 1.87
Stock options
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Effect of dilutive securities									111	310	306
Restricted stock based awards
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Effect of dilutive securities									61	71	101