Schedule I - Condensed Statements of Comprehensive Income (Parent Company Only) (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Tax expense (benefit) on actuarial gain (loss), employee benefit plans	$ (5,205)	$ 5,644	$ (9,045)
Tax expense, adjustment for items reclassified to earnings, employee benefit plans	1,757	1,507	1,923
Parent Company [Member]
Tax expense (benefit) on actuarial gain (loss), employee benefit plans	(5,205)	5,644	(9,045)
Tax expense, adjustment for items reclassified to earnings, employee benefit plans	$ 1,757	$ 1,507	$ 1,923