Associate (Employee) Benefit Plans - Schedule of Net Periodic Benefit Cost Components of Postretirement Benefits (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Business Acquisition [Line Items]
Service cost	$ 11	$ 14	$ 40	$ 43
Interest cost	16	19	54	57
Prior service cost amortization	(19)	(18)	(57)	(44)
Net gain recognition	(18)	(16)	(52)	(47)
Net periodic benefit cost	(10)	$ (1)	(15)	$ 9
Alliance
Business Acquisition [Line Items]
Service cost	10		30
Interest cost	75		225
Expected Return on Plan Assets	(135)		(405)
Prior service cost amortization	0		0
Net gain recognition	0		0
Net periodic benefit cost	$ (50)		$ (150)