Pension and Employee Benefit Plans - Schedule of Changes in Projected Benefit Obligations (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Change in projected benefit obligation:
Service cost	$ 204	$ 126	$ 58
Interest cost	1,428	676	328
Change in plan assets:
Fair value of plan assets at beginning of year	25,822
Fair value of plan assets at end of year	27,302	25,822
Accumulated other comprehensive income (loss):
Amount recognized in accumulated other comprehensive income (loss)	(4,878)	(826)	(2,188)	(2,167)
Weighted-average assumptions used to determine benefit obligations for the year ended December 31:
Discount rate	4.50%		4.25%
Compensation increase rate	0.00%	0.00%	0.00%
Other Postretirement Benefit Plan, Defined Benefit [Member]
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	32,311	8,535	7,886
Accumulated postretirement benefit obligation
Projected benefit obligation from acquisition		24,364
Service cost	204	126	58
Interest cost	1,428	676	328
Actuarial (gain)/loss	6,015	(509)	629
Administrative expenses	(174)	(126)
Benefits paid	(1,576)	(755)	(366)
Projected benefit obligation at end of year	38,208	32,311	8,535
Change in plan assets:
Fair value of plan assets at beginning of year	25,822	5,549	5,020
Fair value of plan assets from acquisition		18,654
Actual return on plan assets	1,404	2,291	603
Employer contribution	1,826	209	292
Administrative expenses	(174)	(126)
Benefits paid	(1,576)	(755)	(366)
Fair value of plan assets at end of year	27,302	25,822	5,549
Funded status	(10,906)	(6,489)	(2,986)
Defined benefit liabilities included in other liabilities	(10,906)	(6,489)	(2,986)
Deferred tax benefit (expense) associated with accumulated other comprehensive loss (income)	2,983	608	1,505
Accumulated other comprehensive loss (income), net of tax	4,865	856	2,257
Net amount recognized	(3,058)	(5,025)	776
Other comprehensive income (loss):
Net loss (gain)	6,561	(1,926)	404
Amortization of prior service cost	(4)	(1)	(1)
Amortization of net actuarial loss	(173)	(370)	(332)
Total recognized in other comprehensive income	6,384	(2,297)	71
Accumulated other comprehensive income (loss):
Net (gain) loss	7,848	1,460	3,757
Prior service cost		4	5
Amount recognized in accumulated other comprehensive income (loss)	7,848	1,464	3,761
Weighted-average assumptions used to determine benefit obligations for the year ended December 31:
Discount rate	3.75%	4.50%	3.75%
Compensation increase rate	0.00%	0.00%	0.00%
Pension Plan [Member]
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	116	89
Accumulated postretirement benefit obligation	116	89	146
Interest cost	5	3	6
Amendments	24	44
Actuarial (gain)/loss	38	8	(43)
Benefits paid	(28)	(28)	(20)
Projected benefit obligation at end of year	155	116	89
Change in plan assets:
Employer contribution	28	28	20
Benefits paid	(28)	(28)	(20)
Funded status	(155)	(116)	(89)
Defined benefit liabilities included in accounts payable and accrued expenses	(25)	(21)	(15)
Defined benefit liabilities included in other liabilities	(130)	(95)	(74)
Deferred tax benefit (expense) associated with accumulated other comprehensive loss (income)	8	(18)	(45)
Accumulated other comprehensive loss (income), net of tax	14	(27)	(67)
Net amount recognized	(133)	(161)	(201)
Other comprehensive income (loss):
Net loss (gain)	38	8	(43)
Prior service cost	24	44
Amortization of prior service cost	(6)
Amortization of net actuarial loss	11	14	8
Total recognized in other comprehensive income	67	66	(35)
Accumulated other comprehensive income (loss):
Net (gain) loss	(40)	(89)	(112)
Prior service cost	62	44
Amount recognized in accumulated other comprehensive income (loss)	$ 22	$ (45)	$ (112)
Weighted-average assumptions used to determine benefit obligations for the year ended December 31:
Discount rate	3.75%	4.50%	3.75%
Compensation increase rate	0.00%	0.00%	0.00%