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, 2016	Mar. 31, 2015
Defined Contribution Plan Disclosure [Line Items]
Total defined contribution expense	$ 3,008	$ 2,164
Retirement Savings Plans [Member]
Defined Contribution Plan Disclosure [Line Items]
Total defined contribution expense	1,291	1,184
Profit Sharing Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Total defined contribution expense	$ 1,717	$ 980