Employee Benefit Plans - Employee Benefit Plans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service cost	$ (14)		$ (45)
Amortization of net loss	172		517
Chesapeake Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	102	125	307	375
Expected return on plan assets	(126)	(108)	(378)	(326)
Amortization of prior service cost	0	(1)	(1)	(4)
Amortization of net loss	57	85	171	255
Net periodic cost (benefit)	33	101	99	300
Total periodic cost	33	101	99	300
FPU Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	594	638	1,782	1,916
Expected return on plan assets	(719)	(658)	(2,156)	(1,973)
Amortization of net loss	81	43	243	131
Net periodic cost (benefit)	(44)	23	(131)
Amortization of pre-merger regulatory asset	191	190	571	571
Total periodic cost	147	213	440	645
Chesapeake Pension SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	21	23	62	68
Amortization of prior service cost	5	5	14	15
Amortization of net loss	16	11	48	34
Net periodic cost (benefit)	42	39	124
Total periodic cost	42	39	124	117
Chesapeake Postretirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	12	15	36	45
Amortization of prior service cost	(19)	(20)	(58)	(60)
Amortization of net loss	18	18	55	53
Net periodic cost (benefit)	11	13	33	38
Total periodic cost	11	13	33	38
FPU Medical Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	40	0	120
Interest cost	16	45	47	135
Amortization of net loss	0	23	0	68
Net periodic cost (benefit)	16	108	47	323
Amortization of pre-merger regulatory asset	2	2	6	6
Total periodic cost	$ 18	$ 110	$ 53	$ 329