Pension and Employee Benefit Plans - Schedule of Changes in Projected Benefit Obligations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in projected benefit obligation:
Service cost		$ 415	$ 447
Interest cost	$ 1,190	1,314	1,426
Change in plan assets:
Fair value of plan assets at beginning of year	26,836
Fair value of plan assets at end of year	24,197	26,836
Other comprehensive (loss) income:
Amount recognized in accumulated other comprehensive (loss) income - Prior service cost	$ (6,245)	$ (5,161)	$ (5,083)	$ (5,170)
Weighted-average assumptions used to determine benefit obligations for the year ended December 31:
Discount rate	3.35%	3.85%	4.00%
Pension Benefits [Member]
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	$ 36,327	$ 35,012	$ 36,140
Service cost		415	447
Interest cost	1,190	1,314	1,426
Actuarial (gain) / loss	(2,629)	1,787	301
Administrative expenses		(402)	(606)
Benefits paid	(1,890)	(1,799)	(2,696)
Projected benefit obligation at end of year	32,998	36,327	35,012
Change in plan assets:
Fair value of plan assets at beginning of year	26,836	24,063	25,296
Actual (loss) return on plan assets	(1,388)	3,152	2,040
Employer contribution	639	1,822	29
Administrative expenses		(402)	(606)
Benefits paid	(1,890)	(1,799)	(2,696)
Fair value of plan assets at end of year	24,197	26,836	24,063
Unfunded status	(8,801)	(9,491)	(10,949)
Defined benefit liability included in other liabilities	(8,801)	(9,491)	(10,949)
Deferred tax benefit associated with accumulated other comprehensive loss	2,116	3,153	3,107
Accumulated other comprehensive loss, net of tax	6,224	5,154	5,074
Other comprehensive (loss) income:
Net loss (gain)	271	358	90
Amortization of net actuarial gain	(238)	(227)	(212)
Total recognized in other comprehensive (loss) income	33	131	(122)
Amount recognized in accumulated other comprehensive (loss) income - Prior service cost	$ 8,340	$ 8,307	$ 8,181
Weighted-average assumptions used to determine benefit obligations for the year ended December 31:
Discount rate	4.05%	3.35%	3.85%