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, 2014		Dec. 31, 2013		Dec. 31, 2012
Change in plan assets:
Balance, end of year	$ 54,155		$ 53,080
Chesapeake Pension Plan
Change in benefit obligation:
Benefit obligation - beginning of year	10,268		11,933
Interest cost	425		405		458
Actuarial loss	1,891		(1,092)
Benefits paid	(603)		(978)
Benefit obligation - end of year	11,981		10,268		11,933
Change in plan assets:
Balance, beginning of year	8,743		8,430
Actual return on plan assets	305		967
Employer contributions	633		324
Benefits paid	(603)		(978)
Balance, end of year	9,078		8,743		8,430
Reconciliation:
Funded status	(2,903)		(1,525)
Accrued pension cost	(2,903)		(1,525)
Assumptions:
Discount rate	4.25%		3.50%		4.25%
Discount rate	3.50%		4.25%
Expected return on plan assets	6.00%		6.00%		6.00%
FPU Pension Plan
Change in benefit obligation:
Benefit obligation - beginning of year	55,876		64,512
Interest cost	2,613		2,367		2,577
Actuarial loss	12,785		(8,007)
Benefits paid	(3,101)		(2,996)
Benefit obligation - end of year	68,173		55,876		64,512
Change in plan assets:
Balance, beginning of year	44,337		41,954
Actual return on plan assets	1,485		4,747
Employer contributions	2,356		632
Benefits paid	(3,101)		(2,996)
Balance, end of year	45,077		44,337		41,954
Reconciliation:
Funded status	(23,096)		(11,539)
Accrued pension cost	(23,096)		(11,539)
Assumptions:
Discount rate	4.75%		3.75%		4.50%
Discount rate	3.75%		4.75%
Expected return on plan assets	7.00%		7.00%		7.00%
Chesapeake SERP
Change in benefit obligation:
Benefit obligation - beginning of year	2,210		2,352
Interest cost	92		81		90
Actuarial loss	437		(134)
Benefits paid	(89)		(89)
Benefit obligation - end of year	2,650		2,210		2,352
Change in plan assets:
Employer contributions	89		89
Benefits paid	(89)		(89)
Reconciliation:
Funded status	(2,650)		(2,210)
Accrued pension cost	(2,650)		(2,210)
Assumptions:
Discount rate	4.25%		3.50%		4.25%
Discount rate	3.50%		4.25%
Chesapeake Postretirement Plan
Change in benefit obligation:
Benefit obligation - beginning of year	1,262		1,415
Service cost	0		0		0
Interest cost	39		47		55
Plan participants contributions	106		92
Actuarial loss	6		(108)
Benefits paid	(175)		(184)
Benefit obligation - end of year	1,238		1,262		1,415
Change in plan assets:
Balance, beginning of year	0		0
Employer contributions	69	[1]	92	[1]
Plan participants contributions	106		92
Benefits paid	(175)		(184)
Balance, end of year	0		0		0
Reconciliation:
Funded status	(1,238)		(1,262)
Accrued pension cost	(1,238)		(1,262)
Assumptions:
Discount rate	4.25%		3.50%		4.25%
Discount rate	3.50%		4.25%
FPU Medical Plan
Change in benefit obligation:
Benefit obligation - beginning of year	1,519		1,774
Service cost	0		0		1
Interest cost	69		63		79
Plan participants contributions	97		104
Actuarial loss	375		(165)
Benefits paid	(348)		(257)
Benefit obligation - end of year	1,712		1,519		1,774
Change in plan assets:
Balance, beginning of year	0		0
Employer contributions	251	[1]	153	[1]
Plan participants contributions	97		104
Benefits paid	(348)		(257)
Balance, end of year	0		0		0
Reconciliation:
Funded status	(1,712)		(1,519)
Accrued pension cost	$ (1,712)		$ (1,519)
Assumptions:
Discount rate	4.75%		3.75%		4.50%
Discount rate	3.75%		4.75%

[1] Chesapeake’s Postretirement Plan does not receive a Medicare Part-D subsidy. The FPU Medical Plan did not receive a significant subsidy for the post-merger period.