Taxes on Income - Schedule of Components of Income Tax Expense (Benefit) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current income taxes:
Federal taxes	$ 36,005	$ 23,857	$ 24,237
State and local taxes	4,342	3,847	3,805
Deferred income taxes:
Federal taxes	17,899	5,135	2,283
State and local taxes	0	235	(52)
Total	$ 58,246	$ 33,074	$ 30,273