Computation of Earnings Per Share (Detail) - $ / shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share Basic And Diluted [Line Items]
Basic earnings per share, Weighted Average Shares	84,005	83,832	83,950	83,748
Potential dilutive effect of restricted stock options outstanding, Weighted Average Shares	126	136	181	194
Diluted earnings per share, Weighted Average Shares	84,131	83,968	84,131	83,942
Basic earnings per share, Earnings per Share	$ 0.92	$ 0.73	$ 2.12	$ 2.14
Potential dilutive effect of restricted stock options outstanding, Earnings per Share	0	0	0.00	(0.01)
Diluted earnings per share, Earnings per Share	$ 0.92	$ 0.73	$ 2.12	$ 2.13