Reconciliation of Net Income and Share Amounts in Computation of Basic and Diluted Net Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Net income	$ 27,897	$ 22,340	$ 77,105	$ 61,646
Earnings per share:
Basic	$ 0.38	$ 0.30	$ 1.05	$ 0.82
Effect of CESs			(0.01)	(0.01)
Diluted	$ 0.38	$ 0.30	$ 1.04	$ 0.81
Weighted average number of shares:
Basic	73,259	74,687	73,616	75,255
Effect of CESs	502	779	546	849
Diluted	73,761	75,466	74,162	76,104