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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income, Basic									$ 178,040	$ 219,919	$ 221,854
Net income, Diluted									$ 178,040	$ 219,919	$ 221,854
Weighted average common shares outstanding, Basic									118,084	117,384	116,949
Weighted average common shares outstanding, Basic									118,084	117,384	116,949
Weighted average shares and assumed conversions									118,465	117,791	117,785
BASIC EARNINGS PER SHARE	$ 0.35	$ 0.35	$ 0.38	$ 0.42	$ 0.52	$ 0.47	$ 0.49	$ 0.39	$ 1.51	$ 1.87	$ 1.90
DILUTED EARNINGS PER SHARE	$ 0.35	$ 0.35	$ 0.38	$ 0.42	$ 0.52	$ 0.47	$ 0.49	$ 0.39	$ 1.50	$ 1.87	$ 1.88
Stock options
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Effect of dilutive securities									310	306	631
Restricted stock based awards
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Effect of dilutive securities									71	101	205