Treasury Stock Acquisition (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($) shares
Schedule of Treasury Stock [Line Items]
Treasury shares at beginning of period | shares	43,392,617
Treasury shares at end of period | shares	43,585,820
Treasury shares at beginning of period	$ 911,094
Treasury stock acquired, cost	3,950
Treasury shares at end of period	$ 915,044
Stock Buyback Program
Schedule of Treasury Stock [Line Items]
Treasury stock acquired, shares | shares	5,503
Treasury stock acquired, cost	$ 109
Long Term Incentive Plan
Schedule of Treasury Stock [Line Items]
Treasury stock acquired, shares | shares	187,700
Treasury stock acquired, cost	$ 3,841