Postretirement Benefit Plans - Defined Contribution Plan Expenses for the Company's Retirement Savings Plans and Profit Sharing Plan (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Defined Contribution Plan Disclosure [Line Items]
Total defined contribution expense	$ 3,102	$ 3,008
Retirement Savings Plans [Member]
Defined Contribution Plan Disclosure [Line Items]
Total defined contribution expense	1,259	1,291
Profit Sharing Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Total defined contribution expense	$ 1,843	$ 1,717