Employee Benefit Plans - Schedule of Funded Status of Benefit Obligation and Plan Assets (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Change in plan assets:
Balance, beginning of year		$ 54,155
Balance, end of year		50,959	$ 54,155
Chesapeake Pension Plan
Change in benefit obligation:
Benefit obligation - beginning of year		11,981	10,268
Interest cost		407	425	$ 405
Actuarial loss		(401)	1,891
Benefits paid		(486)	(603)
Benefit obligation - end of year		11,501	11,981	10,268
Change in plan assets:
Balance, beginning of year		9,078	8,743
Actual return on plan assets		(289)	305
Employer contributions		449	633
Benefits paid		(486)	(603)
Balance, end of year		8,752	9,078	$ 8,743
Reconciliation:
Funded status		(2,749)	(2,903)
Accrued pension cost		$ (2,749)	$ (2,903)
Assumptions:
Discount rate		3.50%	4.25%	3.50%
Discount rate		3.75%	3.50%
Expected return on plan assets		6.00%	6.00%	6.00%
FPU Pension Plan
Change in benefit obligation:
Benefit obligation - beginning of year		$ 68,173	$ 55,876
Interest cost		2,504	2,613	$ 2,367
Actuarial loss		(3,374)	12,785
Benefits paid		(2,868)	(3,101)
Benefit obligation - end of year		64,435	68,173	55,876
Change in plan assets:
Balance, beginning of year		45,077	44,337
Actual return on plan assets		(1,464)	1,485
Employer contributions		1,462	2,356
Benefits paid		(2,868)	(3,101)
Balance, end of year		42,207	45,077	$ 44,337
Reconciliation:
Funded status		(22,228)	(23,096)
Accrued pension cost		$ (22,228)	$ (23,096)
Assumptions:
Discount rate		3.75%	4.75%	3.75%
Discount rate		4.00%	3.75%
Expected return on plan assets		7.00%	7.00%	7.00%
Chesapeake SERP
Change in benefit obligation:
Benefit obligation - beginning of year		$ 2,650	$ 2,210
Interest cost		91	92	$ 81
Actuarial loss		(85)	437
Benefits paid		(146)	(89)
Benefit obligation - end of year		2,510	2,650	$ 2,210
Change in plan assets:
Employer contributions		146	89
Benefits paid		(146)	(89)
Reconciliation:
Funded status		(2,510)	(2,650)
Accrued pension cost		$ (2,510)	$ (2,650)
Assumptions:
Discount rate		3.50%	4.25%	3.50%
Discount rate		3.75%	3.50%
Chesapeake Postretirement Plan
Change in benefit obligation:
Benefit obligation - beginning of year		$ 1,238	$ 1,262
Interest cost		42	39	$ 47
Plan participants contributions		108	106
Actuarial loss		(58)	6
Benefits paid		(177)	(175)
Benefit obligation - end of year		1,153	1,238	1,262
Change in plan assets:
Balance, beginning of year		0	0
Employer contributions	[1]	69	69
Plan participants contributions		108	106
Benefits paid		(177)	(175)
Balance, end of year		0	0	$ 0
Reconciliation:
Funded status		(1,153)	(1,238)
Accrued pension cost		$ (1,153)	$ (1,238)
Assumptions:
Discount rate		3.50%	4.25%	3.50%
Discount rate		3.75%	3.50%
FPU Medical Plan
Change in benefit obligation:
Benefit obligation - beginning of year		$ 1,712	$ 1,519
Interest cost		57	69	$ 63
Plan participants contributions		75	97
Actuarial loss		(132)	375
Benefits paid		(268)	(348)
Benefit obligation - end of year		1,444	1,712	1,519
Change in plan assets:
Balance, beginning of year		0	0
Employer contributions	[1]	193	251
Plan participants contributions		75	97
Benefits paid		(268)	(348)
Balance, end of year		0	0	$ 0
Reconciliation:
Funded status		(1,444)	(1,712)
Accrued pension cost		$ (1,444)	$ (1,712)
Assumptions:
Discount rate		3.75%	4.75%	3.75%
Discount rate		4.00%	3.75%

[1] The Chesapeake 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.