Summary of Significant Accounting Policies - Computation of Basic EPS to Dilutive EPS (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net earnings	$ 104,774	$ 100,381	$ 89,559
Effect of stock options and stock grants, Net Earnings	0	0	0
Net earnings per share, assuming dilution, Net Earnings	$ 104,774	$ 100,381	$ 89,559
Net earnings per share, basic, Weighted Average Shares	66,013,004	64,892,934	64,047,803
Effect of stock options and stock grants, Weighted Average Shares	89,882	175,096	260,732
Net earnings per share, assuming dilution, Weighted Average Shares	66,102,886	65,068,030	64,308,535
Net earnings per share, basic, Per Share Amount	$ 1.59	$ 1.55	$ 1.40
Effect of stock options and stock grants, Per Share Amount		(0.01)	(0.01)
Net earnings per share, assuming dilution, Per Share Amount	$ 1.59	$ 1.54	$ 1.39