Employee Benefit Plans - Additional Information (Detail) (USD $)	3 Months Ended			3 Months Ended
	Mar. 31, 2013	Mar. 31, 2013 Chesapeake Pension Plan [Member]	Dec. 31, 2012 Chesapeake Pension Plan [Member]	Mar. 31, 2013 Chesapeake Pension SERP [Member]	Mar. 31, 2013 FPU Pension Plan [Member]	Mar. 31, 2013 Chesapeake Postretirement Plan [Member]	Mar. 31, 2012 FPU Medical Plan [Member]	Mar. 31, 2013 FPU Medical Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected pension and postretirement benefit costs	$ 999,000
Expected amortization of pre merger regulatory asset	769,000
Unamortized balance of regulatory asset		5,000,000	5,200,000
Contribution to pension plan		364,000		22,000	842,000	22,000	27,000
Additional contribution to pension plan				$ 88,000		$ 97,000		$ 258,000