Employee Benefit Plans - Employee Benefit Plans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service cost	$ (15)		$ (30)
Amortization of net loss	173		344
Chesapeake Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	103	125	205	250
Expected return on plan assets	(126)	(109)	(252)	(218)
Amortization of prior service cost	0	(2)	(1)	(3)
Amortization of net loss	57	85	114	170
Net periodic cost (benefit)	34	99	66	199
Total periodic cost	34	99	66	199
FPU Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	594	639	1,188	1,278
Expected return on plan assets	(718)	(657)	(1,437)	(1,315)
Amortization of net loss	81	44	162	88
Net periodic cost (benefit)	(43)	26	(87)	51
Amortization of pre-merger regulatory asset	191	191	381	381
Total periodic cost	148	217	294	432
Chesapeake Pension SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	20	22	41	45
Amortization of prior service cost	5	5	10	10
Amortization of net loss	16	12	32	23
Net periodic cost (benefit)	41	39	83	78
Total periodic cost	41	39	83	78
Chesapeake Postretirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	12	15	24	30
Amortization of prior service cost	(20)	(20)	(39)	(40)
Amortization of net loss	19	17	36	35
Net periodic cost (benefit)	11	12	21	25
Total periodic cost	11	12	21	25
FPU Medical Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	40	0	80
Interest cost	16	45	32	90
Amortization of net loss	0	22	0	45
Net periodic cost (benefit)	16	107	32	215
Amortization of pre-merger regulatory asset	2	2	4	4
Total periodic cost	$ 18	$ 109	$ 36	$ 219