Associate (Employee) Benefit Plans - Schedule of Net Periodic Benefit Cost Components of Postretirement Benefits (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Business Acquisition [Line Items]
Service cost	$ 14	$ 14	$ 29	$ 29
Interest cost	19	19	38	38
Prior service cost amortization	(19)	(19)	(38)	(26)
Net gain recognition	(18)	(16)	(34)	(31)
Net periodic benefit cost	(4)	$ (2)	(5)	$ 10
Alliance
Business Acquisition [Line Items]
Service cost	10		20
Interest cost	75		150
Expected Return on Plan Assets	(135)		(270)
Prior service cost amortization	0		0
Net gain recognition	0		0
Net periodic benefit cost	$ (50)		$ (100)