Summary of Significant Accounting Policies - Computation of Basic EPS to Dilutive EPS (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net earnings	$ 100,381	$ 89,559	$ 78,868
Effect of stock options and stock grants, Net Earnings	0	0	0
Net earnings per share, assuming dilution, Net Earnings	$ 100,381	$ 89,559	$ 78,868
Net earnings per share, basic, Weighted Average Shares	64,892,934	64,047,803	63,575,948
Effect of stock options and stock grants, Weighted Average Shares	175,096	260,732	280,816
Net earnings per share, assuming dilution, Weighted Average Shares	65,068,030	64,308,535	63,856,764
Net earnings per share, basic, Per Share Amount	$ 1.55	$ 1.40	$ 1.24
Effect of stock options and stock grants, Per Share Amount	(0.01)	(0.01)
Net earnings per share, assuming dilution, Per Share Amount	$ 1.54	$ 1.39	$ 1.24