Employee Benefit Plans - Component of Net Periodic Pension Cost (Benefit) (Detail) (USD $) In Thousands, unless otherwise specified	1 Months Ended	12 Months Ended
	Jan. 31, 2011	Dec. 31, 2012	Dec. 31, 2012 Chesapeake Pension Plan [Member]	Dec. 31, 2011 Chesapeake Pension Plan [Member]	Dec. 31, 2010 Chesapeake Pension Plan [Member]	Dec. 31, 2012 FPU Pension Plan [Member]	Dec. 31, 2011 FPU Pension Plan [Member]	Dec. 31, 2010 FPU Pension Plan [Member]	Dec. 31, 2012 Chesapeake SERP [Member]	Dec. 31, 2011 Chesapeake SERP [Member]	Dec. 31, 2010 Chesapeake SERP [Member]	Dec. 31, 2012 Chesapeake Postretirement Plan [Member]	Dec. 31, 2011 Chesapeake Postretirement Plan [Member]	Dec. 31, 2010 Chesapeake Postretirement Plan [Member]	Dec. 31, 2012 FPU Medical Plan [Member]	Dec. 31, 2011 FPU Medical Plan [Member]	Dec. 31, 2010 FPU Medical Plan [Member]
Components of net periodic cost:
Service cost															$ 1	$ 125	$ 76
Interest cost			458	520	570	2,577	2,695	2,729	90	107	136	55	64	122	79	176	123
Expected return on assets			(418)	(424)	(423)	(2,627)	(2,783)	(2,532)
Amortization of prior service cost			(5)	(5)	(5)				19	19	18	(77)	(77)
Actuarial (gain) loss			255	156	155	196			46	38	59	73	67	57		55	(6)
Net periodic pension cost			290	247	297	146	(88)	197	155	164	213	51	54	179	80	356	193
Settlement expense	(436)			217						219
Curtailment gain															(892)
Amortization of pre-merger regulatory asset		769				761	761	888							8
Net periodic postretirement cost			$ 290	$ 464	$ 297	$ 907	$ 673	$ 1,085	$ 155	$ 383	$ 213	$ 51	$ 54	$ 179	$ (812)	$ 356	$ 193
Assumptions
Discount rate			4.25%	5.00%	5.25%	4.50%	5.25%	5.75%	4.25%	5.00%	5.25%	4.25%	5.00%	5.25%	4.50%	5.25%	5.75%
Expected return on plan assets			6.00%	6.00%	6.00%	7.00%	7.00%	7.00%