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		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Defined Contribution Plan Disclosure [Line Items]
Total defined contribution expense	$ 3,040	$ 2,347	$ 6,048	$ 4,511
Retirement Savings Plans [Member]
Defined Contribution Plan Disclosure [Line Items]
Total defined contribution expense	1,254	1,136	2,545	2,320
Profit Sharing Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Total defined contribution expense	$ 1,786	$ 1,211	$ 3,503	$ 2,191