Employee Benefit Plans - Component of Net Periodic Pension Cost (Benefit) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Components of net periodic cost:
Expected Amortization Of Pre Merger Regulatory Asset	$ 0
Amortization of pre-merger regulatory asset	769
Chesapeake Pension Plan
Components of net periodic cost:
Interest cost	407	$ 425	$ 405
Expected return on assets	(530)	(516)	(486)
Amortization of prior service cost	0	0	(1)
Actuarial (gain) loss	392	176	322
Net periodic pension cost	269	85	240
Amortization of pre-merger regulatory asset	0	0	0
Net periodic postretirement cost	$ 269	$ 85	$ 240
Assumptions
Discount rate	3.50%	4.25%	3.50%
Expected return on plan assets	6.00%	6.00%	6.00%
FPU Pension Plan
Components of net periodic cost:
Interest cost	$ 2,504	$ 2,613	$ 2,367
Expected return on assets	(3,107)	(3,089)	(2,866)
Amortization of prior service cost	0	0	0
Actuarial (gain) loss	456	8	330
Net periodic pension cost	(147)	(468)	(169)
Amortization of pre-merger regulatory asset	761	761	761
Net periodic postretirement cost	$ 614	$ 293	$ 592
Assumptions
Discount rate	3.75%	4.75%	3.75%
Expected return on plan assets	7.00%	7.00%	7.00%
Chesapeake SERP
Components of net periodic cost:
Interest cost	$ 91	$ 92	$ 81
Amortization of prior service cost	9	19	19
Actuarial (gain) loss	99	47	64
Amortization of pre-merger regulatory asset	0
Net periodic postretirement cost	$ 199	$ 158	$ 164
Assumptions
Discount rate	3.50%	4.25%	3.50%
Chesapeake Postretirement Plan
Components of net periodic cost:
Interest cost	$ 42	$ 39	$ 47
Amortization of prior service cost	(77)	(77)	(77)
Actuarial (gain) loss	72	55	74
Net periodic pension cost	37	17	44
Expected Amortization Of Pre Merger Regulatory Asset		0	0
Amortization of pre-merger regulatory asset	0
Net periodic postretirement cost	$ 37	$ 17	$ 44
Assumptions
Discount rate	3.50%	4.25%	3.50%
FPU Medical Plan
Components of net periodic cost:
Interest cost	$ 57	$ 69	$ 63
Amortization of prior service cost	0	0	0
Actuarial (gain) loss	0	0	0
Net periodic pension cost	57	69	63
Amortization of pre-merger regulatory asset	8	8	8
Net periodic postretirement cost	$ 65	$ 77	$ 71
Assumptions
Discount rate	3.75%	4.75%	3.75%