Employee Benefit Plans - Schedule of Funded Status of Benefit Obligation and Plan Assets (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in benefit obligation:
Interest cost		$ 74	$ 83	$ 89
Change in plan assets:
Balance, beginning of year		52,250
Balance, end of year		54,333	52,250
Chesapeake Pension Plan
Change in benefit obligation:
Benefit obligation - beginning of year		10,712	11,443
Interest cost		375	384	402
Actuarial loss		1,443	(610)
Defined Benefit Plan, Benefit Obligation, Payment for Settlement		(5,833)
Benefits paid		(483)	(505)
Benefit obligation - end of year		6,214	10,712	11,443
Change in plan assets:
Balance, beginning of year		8,649	9,350
Actual return on plan assets		1,180	(647)
Employer contributions		1,117	451
Defined Benefit Plan, Plan Assets, Payment for Settlement		(5,833)
Benefits paid		(483)	(505)
Balance, end of year		4,630	8,649	$ 9,350
Reconciliation:
Funded status		(1,584)	(2,063)
Accrued pension cost		$ (1,584)	$ (2,063)
Assumptions:
Discount rate		3.00%	4.00%
Expected return on plan assets		6.00%	6.00%	6.00%
FPU Pension Plan
Change in benefit obligation:
Benefit obligation - beginning of year		$ 59,377	$ 64,664
Interest cost		2,452	2,339	$ 2,482
Actuarial loss		6,508	(4,739)
Benefits paid		(3,033)	(2,887)
Benefit obligation - end of year		65,304	59,377	64,664
Change in plan assets:
Balance, beginning of year		43,601	48,396
Actual return on plan assets		7,978	(3,113)
Employer contributions		1,157	1,205
Benefits paid		(3,033)	(2,887)
Balance, end of year		49,703	43,601	$ 48,396
Reconciliation:
Funded status		(15,601)	(15,776)
Accrued pension cost		$ (15,601)	$ (15,776)
Assumptions:
Discount rate		3.25%	4.25%
Expected return on plan assets		6.50%	6.50%	6.50%
Chesapeake SERP
Change in benefit obligation:
Benefit obligation - beginning of year		$ 2,285	$ 2,428
Interest cost		74	83
Actuarial loss		159	(74)
Benefits paid		(361)	(152)
Benefit obligation - end of year		2,157	2,285	$ 2,428
Change in plan assets:
Employer contributions		361	152
Benefits paid		(361)	(152)
Reconciliation:
Funded status		(2,157)	(2,285)
Accrued pension cost		$ (2,157)	$ (2,285)
Assumptions:
Discount rate		3.00%	4.00%
Chesapeake Postretirement Plan
Change in benefit obligation:
Benefit obligation - beginning of year		$ 1,002	$ 1,128
Interest cost		39	38	41
Plan participants contributions		149	136
Actuarial loss		73	(131)
Benefits paid		(163)	(169)
Benefit obligation - end of year		1,100	1,002	1,128
Change in plan assets:
Balance, beginning of year		0	0
Employer contributions	[1]	14	33
Plan participants contributions		149	136
Benefits paid		(163)	(169)
Balance, end of year		0	0	0
Reconciliation:
Funded status		(1,100)	(1,002)
Accrued pension cost		$ (1,100)	$ (1,002)
Assumptions:
Discount rate		3.00%	4.00%
FPU Medical Plan
Change in benefit obligation:
Benefit obligation - beginning of year		$ 1,187	$ 1,287
Interest cost		48	47	50
Plan participants contributions		38	41
Actuarial loss		47	(89)
Benefits paid		(96)	(99)
Benefit obligation - end of year		1,224	1,187	1,287
Change in plan assets:
Balance, beginning of year		0	0
Employer contributions	[1]	58	58
Plan participants contributions		38	41
Benefits paid		(96)	(99)
Balance, end of year		0	0	$ 0
Reconciliation:
Funded status		(1,224)	(1,187)
Accrued pension cost		$ (1,224)	$ (1,187)
Assumptions:
Discount rate		3.25%	4.25%

[1] The Chesapeake Postretirement Plan does not receive a Medicare Part-D subsidy. The FPU Medical Plan did not receive a significant subsidy for the post-merger period.