Employee Benefit Plans - Additional Information (Detail) (USD $)	9 Months Ended	3 Months Ended	9 Months Ended		3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	6 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012 Chesapeake Pension Plan [Member]	Sep. 30, 2012 Chesapeake Pension Plan [Member]	Dec. 31, 2011 Chesapeake Pension Plan [Member]	Sep. 30, 2012 FPU Pension Plan [Member]	Sep. 30, 2012 FPU Pension Plan [Member]	Sep. 30, 2012 Chesapeake Pension SERP [Member]	Sep. 30, 2012 Chesapeake Pension SERP [Member]	Sep. 30, 2012 Chesapeake Postretirement Plan [Member]	Sep. 30, 2012 Chesapeake Postretirement Plan [Member]	Sep. 30, 2012 Chesapeake Postretirement Plan [Member]	Sep. 30, 2012 FPU Medical Plan [Member]	Sep. 30, 2012 FPU Medical Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected pension and postretirement benefit costs	$ 1,900,000
Expected amortization of pre merger regulatory asset	769,000
Unamortized balance of regulatory asset		5,400,000	5,400,000	5,900,000
Period of average for corporate bond rate to measure pension obligations for pension funding purposes	25 years
Contribution to pension plan		1,100,000	1,300,000		1,900,000	2,600,000	22,000	67,000	20,000	60,000	60,000	40,000	198,000
Additional contribution to pension plan							$ 88,000	$ 88,000	$ 87,000	$ 87,000	$ 87,000	$ 193,000	$ 193,000