Employee Benefit Plans - Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Retirement Benefits [Abstract]
Current year actuarial loss	$ (27,672)	$ 152,415	$ 44,930
Recognition of actuarial loss	(38,034)	(31,641)	(38,197)
Current year prior service cost	4,768	2,063	0
Recognition of prior service credit	350	432	565
Total recognized in other comprehensive (loss) income	(60,588)	123,269	7,298
Total recognized in net periodic benefit income and other comprehensive (loss) income	$ (73,226)	$ 109,877	$ 1,450