Treasury Stock Acquisition (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Treasury Stock [Line Items]
Treasury shares at beginning of period	43,207,240	42,818,585	42,268,057
Treasury shares at end of period	43,392,617	43,207,240	42,818,585
Treasury shares at beginning of period	$ 907,045	$ 899,035	$ 880,888
Treasury stock acquired, cost	4,049	8,010	18,147
Treasury shares at end of period	$ 911,094	$ 907,045	$ 899,035
2013 Stock Buyback Program
Schedule of Treasury Stock [Line Items]
Treasury stock acquired, shares	8,488	8,618	13,898
Treasury stock acquired, cost	$ 183	$ 180	$ 466
Long Term Incentive Plan
Schedule of Treasury Stock [Line Items]
Treasury stock acquired, shares	176,889	380,037	536,630
Treasury stock acquired, cost	$ 3,866	$ 7,830	$ 17,681