Employee Benefit Plans - Schedule of Funded Status of Benefit Obligation and Plan Assets (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in benefit obligation:
Interest cost		$ 83	$ 89	$ 91
Change in plan assets:
Balance, beginning of year		57,746
Balance, end of year		52,250	57,746
Chesapeake Pension Plan
Change in benefit obligation:
Benefit obligation - beginning of year		11,443	11,355
Interest cost		384	402	421
Actuarial loss		(610)	454
Benefits paid		(505)	(768)
Benefit obligation - end of year		10,712	11,443	11,355
Change in plan assets:
Balance, beginning of year		9,350	8,668
Actual return on plan assets		(647)	1,144
Employer contributions		451	306
Benefits paid		(505)	(768)
Balance, end of year		8,649	9,350	$ 8,668
Reconciliation:
Funded status		(2,063)	(2,093)
Accrued pension cost		$ (2,063)	$ (2,093)
Assumptions:
Discount rate		4.00%	3.50%
Expected return on plan assets		6.00%	6.00%	6.00%
FPU Pension Plan
Change in benefit obligation:
Benefit obligation - beginning of year		$ 64,664	$ 63,832
Interest cost		2,339	2,482	$ 2,525
Actuarial loss		(4,739)	1,199
Benefits paid		(2,887)	(2,849)
Benefit obligation - end of year		59,377	64,664	63,832
Change in plan assets:
Balance, beginning of year		48,396	43,272
Actual return on plan assets		(3,113)	6,025
Employer contributions		1,205	1,948
Benefits paid		(2,887)	(2,849)
Balance, end of year		43,601	48,396	$ 43,272
Reconciliation:
Funded status		(15,776)	(16,268)
Accrued pension cost		$ (15,776)	$ (16,268)
Assumptions:
Discount rate		4.25%	3.75%
Expected return on plan assets		6.50%	6.50%	6.50%
Chesapeake SERP
Change in benefit obligation:
Benefit obligation - beginning of year		$ 2,428	$ 2,428
Interest cost		83	89
Actuarial loss		(74)	63
Benefits paid		(152)	(152)
Benefit obligation - end of year		2,285	2,428	$ 2,428
Change in plan assets:
Employer contributions		152	152
Benefits paid		(152)	(152)
Reconciliation:
Funded status		(2,285)	(2,428)
Accrued pension cost		$ (2,285)	$ (2,428)
Assumptions:
Discount rate		4.00%	3.50%
Chesapeake Postretirement Plan
Change in benefit obligation:
Benefit obligation - beginning of year		$ 1,128	$ 1,132
Interest cost		38	41	43
Plan participants contributions		136	118
Actuarial loss		(131)	72
Benefits paid		(169)	(235)
Benefit obligation - end of year		1,002	1,128	1,132
Change in plan assets:
Balance, beginning of year		0	0
Employer contributions	[1]	33	117
Plan participants contributions		136	118
Benefits paid		(169)	(235)
Balance, end of year		0	0	0
Reconciliation:
Funded status		(1,002)	(1,128)
Accrued pension cost		$ (1,002)	$ (1,128)
Assumptions:
Discount rate		4.00%	3.50%
FPU Medical Plan
Change in benefit obligation:
Benefit obligation - beginning of year		$ 1,287	$ 1,349
Interest cost		47	50	55
Plan participants contributions		41	48
Actuarial loss		(89)	(48)
Benefits paid		(99)	(112)
Benefit obligation - end of year		1,187	1,287	1,349
Change in plan assets:
Balance, beginning of year		0	0
Employer contributions	[1]	58	64
Plan participants contributions		41	48
Benefits paid		(99)	(112)
Balance, end of year		0	0	$ 0
Reconciliation:
Funded status		(1,187)	(1,287)
Accrued pension cost		$ (1,187)	$ (1,287)
Assumptions:
Discount rate		4.25%	3.75%

[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.