Employee Benefit Plans - Schedule of Funded Status of Benefit Obligation and Plan Assets (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Change in plan assets:
Balance, beginning of year	$ 44,998
Employer contributions	2,900	2,700	1,700
Balance, end of year	50,384	44,998
Chesapeake Pension Plan [Member]
Change in benefit obligation:
Benefit obligation - beginning of year	11,672	11,760
Interest cost	458	520	570
Actuarial loss	726	941
Benefits paid	(923)	(705)
Effect of settlement		(844)
Benefit obligation - end of year	11,933	11,672	11,760
Change in plan assets:
Balance, beginning of year	7,162	7,787
Actual return on plan assets	849	(124)
Employer contributions	1,342	1,048
Benefits paid	(923)	(705)
Effect of settlement		(844)
Balance, end of year	8,430	7,162	7,787
Reconciliation:
Funded status	(3,503)	(4,510)
Accrued pension cost	(3,503)	(4,510)
Assumptions:
Discount rate	4.25%	5.00%	5.25%
Discount rate	3.50%	4.25%
Expected return on plan assets	6.00%	6.00%
FPU Pension Plan [Member]
Change in benefit obligation:
Benefit obligation - beginning of year	57,999	52,478
Interest cost	2,577	2,695	2,729
Actuarial loss	6,915	5,403
Benefits paid	(2,979)	(2,577)
Benefit obligation - end of year	64,512	57,999	52,478
Change in plan assets:
Balance, beginning of year	37,836	40,201
Actual return on plan assets	4,526	(1,101)
Employer contributions	2,571	1,313
Benefits paid	(2,979)	(2,577)
Balance, end of year	41,954	37,836	40,201
Reconciliation:
Funded status	(22,558)	(20,163)
Accrued pension cost	(22,558)	(20,163)
Assumptions:
Discount rate	4.50%	5.25%	5.75%
Discount rate	3.75%	4.50%
Expected return on plan assets	7.00%	7.00%
Chesapeake SERP [Member]
Change in benefit obligation:
Benefit obligation - beginning of year	2,160	2,731
Interest cost	90	107	136
Actuarial loss	191	176
Benefits paid	(89)	(89)
Effect of settlement		(765)
Benefit obligation - end of year	2,352	2,160	2,731
Change in plan assets:
Employer contributions	89	854
Benefits paid	(89)	(89)
Effect of settlement		(765)
Reconciliation:
Funded status	(2,352)	(2,160)
Accrued pension cost	(2,352)	(2,160)
Assumptions:
Discount rate	4.25%	5.00%	5.25%
Discount rate	3.50%	4.25%
Chesapeake Postretirement Plan [Member]
Change in benefit obligation:
Service cost
Interest cost	55	64	122
Assumptions:
Discount rate	4.25%	5.00%	5.25%
Chesapeake Postretirement Plan [Member] | Other Postretirement Benefit Plans [Member]
Change in benefit obligation:
Benefit obligation - beginning of year	1,396	2,474
Interest cost	55	64
Plan amendments		(1,140)
Plan participants contributions	111	108
Actuarial loss	39	100
Benefits paid	(186)	(210)
Benefit obligation - end of year	1,415	1,396
Change in plan assets:
Balance, beginning of year
Employer contributions	75	102
Plan participants contributions	111	108
Benefits paid	(186)	(210)
Balance, end of year
Reconciliation:
Funded status	(1,415)	(1,396)
Accrued pension cost	(1,415)	(1,396)
Assumptions:
Discount rate	3.50%	4.25%
FPU Medical Plan [Member]
Change in benefit obligation:
Service cost	1	125	76
Interest cost	79	176	123
Assumptions:
Discount rate	4.50%	5.25%	5.75%
FPU Medical Plan [Member] | Other Postretirement Benefit Plans [Member]
Change in benefit obligation:
Benefit obligation - beginning of year	4,081	3,098
Service cost	1	125
Interest cost	79	176
Plan participants contributions	92	88
Curtailment gain	(2,651)
Actuarial loss	500	802
Benefits paid	(328)	(208)
Benefit obligation - end of year	1,774	4,081
Change in plan assets:
Balance, beginning of year
Employer contributions	236	120
Plan participants contributions	92	88
Benefits paid	(328)	(208)
Balance, end of year
Reconciliation:
Funded status	(1,774)	(4,081)
Accrued pension cost	$ (1,774)	$ (4,081)
Assumptions:
Discount rate	3.75%	4.50%