Associate Benefit Plans - Additional Information (Detail)		12 Months Ended
	Mar. 31, 2014	Dec. 31, 2018 USD ($) plan shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Cash contributions to the plan on behalf of associates, cash expenditure		$ 3,800,000	$ 3,600,000	$ 3,100,000
Percentage of contributions to be invested in balanced fund if no designation made (as percent)		100.00%
Employee benefit plan, sales of common stock (in shares) | shares		51,000	156,000	36,000
Employee benefit plan purchase of common stock (in shares) | shares		0	83,000	0
Requisite service period	10 years
Amortization of unrecognized gains losses exceed (as percent)		10.00%
Expected amortization of net actuarial gain in next fiscal year		$ 100,000
Expected amortization of net transition obligation in next fiscal year		$ 100,000
Percentage of annual medical premium cap (as percent)		4.00%
Amount of annual health premium per retiree		$ 3,553
Estimated contribution for health fund in next fiscal year			$ 3,695
Benefit obligation		(1,893,000)	(1,990,000)	$ (1,764,000)	$ (1,805,000)
Defined benefit plan fair value of assets		$ 0	0	0	0
Number of additional supplemental plans | plan		5
Supplemental Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plan, corresponding liability (less than)		$ 700,000	700,000
Early Retirement Window Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plan, corresponding liability (less than)		100,000	100,000
Supplemental Executive Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plan, corresponding liability (less than)		1,500,000	1,500,000
Post-Retirement Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plan, corresponding liability (less than)		$ 100,000	100,000
Maximum
Defined Benefit Plan Disclosure [Line Items]
Average annual rate of increase for medical benefits (less than) (as percent)		10.00%
Maximum | Director's Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plan, corresponding asset (less than)		$ 100,000	100,000
Alliance
Defined Benefit Plan Disclosure [Line Items]
Amortization from accumulated other comprehensive income		0
Pennsylvania | Alliance
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation		(6,289,000)	(7,853,000)	(7,517,000)	(7,148,000)
Defined benefit plan fair value of assets		6,533,000	$ 8,378,000	$ 7,504,000	$ 7,397,000
Net amount recognized		$ 300,000