Associate Benefit Plans - Schedule of Net Periodic Benefit Cost Components of Postretirement Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in benefit obligation:
Benefit obligation at beginning of year	$ 1,893	$ 1,990	$ 1,764
Service cost	54	60	53
Interest cost	78	70	71
Actuarial gain (loss)	229	(143)	207
Benefits paid	(84)	(84)	(105)
Benefit obligation at end of year	2,170	1,893	1,990
Change in plan assets:
Fair value of plan assets at beginning of year	0	0	0
Employer contributions	84	84	105
Benefits paid	(84)	(84)	(105)
Fair value of plan assets at end of year	0	0	0
Unfunded status	(2,170)	(1,893)	(1,990)
Amounts recognized in accumulated other comprehensive income:
Net prior service credit	511	587	663
Net (loss) gain	491	783	685
Net amount recognized	1,002	1,370	1,348
Components of net periodic benefit cost:
Service cost	54	60	53
Interest cost	78	70	71
Amortization of prior service cost	(76)	(76)	(76)
Net gain recognition	(63)	(45)	(70)
Net periodic benefit cost	$ (7)	$ 9	$ (22)
Assumption used to value the Accumulated Postretirement Benefit Obligation (APBO):
Discount rate for Net Periodic Benefit Cost (as percent)	4.20%	3.60%	4.10%
Discount rate for Disclosure Obligations (as percent)	3.10%	4.20%	3.60%
Pension Benefits
Assumption used to value the Accumulated Postretirement Benefit Obligation (APBO):
Discount rate for Net Periodic Benefit Cost (as percent)	4.14%
Expected Return on Plan Assets (as percent)	6.50%
Discount rate for Disclosure Obligations (as percent)	3.25%
Other Postretirement Benefits | FMS
Assumption used to value the Accumulated Postretirement Benefit Obligation (APBO):
Discount rate for Net Periodic Benefit Cost (as percent)	3.60%
Discount rate for Disclosure Obligations (as percent)	2.60%
Other Postretirement Benefits | Split-Dollar
Assumption used to value the Accumulated Postretirement Benefit Obligation (APBO):
Discount rate for Net Periodic Benefit Cost (as percent)	3.54%
Discount rate for Disclosure Obligations (as percent)	2.55%
Beneficial | Pension Benefits
Change in benefit obligation:
Benefit obligation at beginning of year	$ 0
Acquired in business combinations	91,568
Service cost	0
Interest cost	2,851
Plan participants' contributions	0
Actuarial gain (loss)	12,020
Benefits paid	(3,561)
Benefit obligation at end of year	102,878	$ 0
Change in plan assets:
Fair value of plan assets at beginning of year	0
Acquired in business combinations	90,814
Actual return on plan assets	13,350
Employer contributions	293
Participants' contributions	0
Benefits paid	(3,561)
Administrative expenses	(508)
Fair value of plan assets at end of year	100,388	0
Unfunded status	(2,490)
Amounts recognized in accumulated other comprehensive income:
Net (loss) gain	(4,174)
Components of net periodic benefit cost:
Service cost	0
Interest cost	2,851
Expected return on plan assets	(4,829)
Net periodic benefit cost	(1,978)
Beneficial | Other Postretirement Benefits
Change in benefit obligation:
Benefit obligation at beginning of year	0
Acquired in business combinations	19,504
Service cost	76
Interest cost	588
Plan participants' contributions	34
Actuarial gain (loss)	1,035
Benefits paid	(974)
Benefit obligation at end of year	20,263	0
Change in plan assets:
Fair value of plan assets at beginning of year	0
Acquired in business combinations	0
Actual return on plan assets	0
Employer contributions	940
Participants' contributions	34
Benefits paid	(974)
Administrative expenses	0
Fair value of plan assets at end of year	0	0
Unfunded status	(20,263)
Amounts recognized in accumulated other comprehensive income:
Net (loss) gain		(1,035)
Components of net periodic benefit cost:
Service cost	76
Interest cost	588
Expected return on plan assets	0
Net periodic benefit cost	$ 664
Assumption used to value the Accumulated Postretirement Benefit Obligation (APBO):
Discount rate for Net Periodic Benefit Cost (as percent)	4.10%
Discount rate for Disclosure Obligations (as percent)	3.19%
Pennsylvania | Alliance
Change in benefit obligation:
Benefit obligation at beginning of year	$ 6,289	7,853	$ 7,517
Service cost	40	40	40
Interest cost	253	279	297
Settlements	(282)	(1,142)	0
Actuarial gain (loss)	864	(430)	446
Benefits paid	(231)	(271)	(407)
Benefit obligation at end of year	6,893	6,289	7,853
Change in plan assets:
Fair value of plan assets at beginning of year	6,533	8,378	7,504
Actual return on plan assets	1,435	(393)	1,314
Settlements	(273)	(1,146)	0
Benefits paid	(231)	(271)	(407)
Administrative expenses	(33)	(35)	(33)
Fair value of plan assets at end of year	7,431	6,533	8,378
Unfunded status	538	244	525
Amounts recognized in accumulated other comprehensive income:
Net (loss) gain	(279)	(413)	170
Components of net periodic benefit cost:
Service cost	40	40	40
Interest cost	253	279	297
Expected return on plan assets	(471)	(596)	(548)
Settlements	16	(24)	0
Net gain recognition	0	413	(170)
Net periodic benefit cost	$ (162)	$ 112	$ (381)
Assumption used to value the Accumulated Postretirement Benefit Obligation (APBO):
Discount rate for Net Periodic Benefit Cost (as percent)	4.20%	3.60%	4.00%
Expected Return on Plan Assets (as percent)	7.50%	7.50%	7.50%
Discount rate for Disclosure Obligations (as percent)	2.40%	4.20%	3.60%