Employee Benefit Plans - Component of Net Periodic Pension Cost (Benefit) (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Components of net periodic cost:
Interest cost		$ 83	$ 89	$ 91
Expected Amortization Of Pre Merger Regulatory Asset		0
Assumptions
Defined Benefit Plan, Plan Assets, Amount		52,250	57,746
Chesapeake Postretirement Plan
Components of net periodic cost:
Interest cost		38	41	43
Amortization of prior service cost		(77)	(77)	(77)
Actuarial (gain) loss		58	53	64
Net periodic pension cost		19	17	30
Expected Amortization Of Pre Merger Regulatory Asset			0	0
Net periodic postretirement cost	[1]	$ 19	$ 17	$ 30
Assumptions
Discount rate		3.50%	3.75%	3.75%
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant		$ 136	$ 118
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)		(131)	72
Defined Benefit Plan, Benefit Obligation, Benefits Paid		(169)	(235)
Defined Benefit Plan, Plan Assets, Amount		0	0	$ 0
Defined Benefit Plan, Plan Assets, Contributions by Employer	[2]	33	117
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant		136	118
Defined Benefit Plan, Plan Assets, Benefits Paid		(169)	(235)
Funded status		(1,002)	(1,128)
Defined Benefit Plan Accrued Pension Costs Accrued Expenses Employment Benefits		$ 1,002	$ 1,128
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		4.00%	3.50%
FPU Medical Plan
Components of net periodic cost:
Interest cost		$ 47	$ 50	55
Amortization of prior service cost		0	0	0
Actuarial (gain) loss		0	0	0
Net periodic pension cost		47	50	55
Amortization of pre-merger regulatory asset		8	8	8
Net periodic postretirement cost	[1]	$ 55	$ 58	$ 63
Assumptions
Discount rate		3.75%	4.00%	4.00%
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant		$ 41	$ 48
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)		(89)	(48)
Defined Benefit Plan, Benefit Obligation, Benefits Paid		(99)	(112)
Defined Benefit Plan, Plan Assets, Amount		0	0	$ 0
Defined Benefit Plan, Plan Assets, Contributions by Employer	[2]	58	64
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant		41	48
Defined Benefit Plan, Plan Assets, Benefits Paid		(99)	(112)
Funded status		(1,187)	(1,287)
Defined Benefit Plan Accrued Pension Costs Accrued Expenses Employment Benefits		$ 1,187	$ 1,287
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		4.25%	3.75%
Chesapeake SERP
Components of net periodic cost:
Interest cost		$ 83	$ 89
Actuarial (gain) loss		101	87	87
Net periodic postretirement cost		$ 184	$ 176	$ 178
Assumptions
Discount rate		3.50%	3.75%	3.75%
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)		$ (74)	$ 63
Defined Benefit Plan, Benefit Obligation, Benefits Paid		(152)	(152)
Defined Benefit Plan, Plan Assets, Contributions by Employer		152	152
Defined Benefit Plan, Plan Assets, Benefits Paid		(152)	(152)
Funded status		(2,285)	(2,428)
Defined Benefit Plan Accrued Pension Costs Accrued Expenses Employment Benefits		$ 2,285	$ 2,428
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		4.00%	3.50%
Chesapeake Pension Plan
Components of net periodic cost:
Interest cost		$ 384	$ 402	$ 421
Expected return on assets		(542)	(495)	(501)
Actuarial (gain) loss		343	399	459
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement		0	0	161
Net periodic pension cost		185	306	540
Amortization of pre-merger regulatory asset		0	0	0
Net periodic postretirement cost		$ 185	$ 306	$ 540
Assumptions
Discount rate		3.50%	3.75%	3.75%
Expected return on plan assets		6.00%	6.00%	6.00%
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)		$ (610)	$ 454
Defined Benefit Plan, Benefit Obligation, Benefits Paid		(505)	(768)
Defined Benefit Plan, Plan Assets, Amount		8,649	9,350	$ 8,668
Defined Benefit Plan, Plan Assets, Contributions by Employer		451	306
Defined Benefit Plan, Plan Assets, Benefits Paid		(505)	(768)
Funded status		(2,063)	(2,093)
Defined Benefit Plan Accrued Pension Costs Accrued Expenses Employment Benefits		$ 2,063	$ 2,093
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		4.00%	3.50%
FPU Pension Plan
Components of net periodic cost:
Interest cost		$ 2,339	$ 2,482	2,525
Expected return on assets		(3,091)	(2,779)	(2,702)
Actuarial (gain) loss		404	513	519
Net periodic pension cost		(348)	216	342
Amortization of pre-merger regulatory asset		761	761	761
Net periodic postretirement cost		$ 413	$ 977	$ 1,103
Assumptions
Discount rate		3.75%	4.00%	4.00%
Expected return on plan assets		6.50%	6.50%	6.50%
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)		$ (4,739)	$ 1,199
Defined Benefit Plan, Benefit Obligation, Benefits Paid		(2,887)	(2,849)
Defined Benefit Plan, Plan Assets, Amount		43,601	48,396	$ 43,272
Defined Benefit Plan, Plan Assets, Contributions by Employer		1,205	1,948
Defined Benefit Plan, Plan Assets, Benefits Paid		(2,887)	(2,849)
Funded status		(15,776)	(16,268)
Defined Benefit Plan Accrued Pension Costs Accrued Expenses Employment Benefits		$ 15,776	$ 16,268
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		4.25%	3.75%

[1] As a result of our adoption of ASU 2017-07 on January 1, 2018, the "other than service" cost components of the net periodic costs have been recorded or reclassified to other income (expense), net in the condensed consolidated statements of income.

[2] 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.